Enforce readonly private members where possible.

osu.Desktop.Deploy/Program.cs

@@ -53,7 +53,7 @@ namespace osu.Desktop.Deploy
         private static string nupkgFilename(string ver) => $"{PackageName}.{ver}.nupkg";
         private static string nupkgDistroFilename(string ver) => $"{PackageName}-{ver}-full.nupkg";
 
-        private static Stopwatch sw = new Stopwatch();
+        private static readonly Stopwatch sw = new Stopwatch();
 
         private static string codeSigningPassword;
 

osu.Desktop.VisualTests/Beatmaps/TestWorkingBeatmap.cs

@@ -15,7 +15,7 @@ namespace osu.Desktop.VisualTests.Beatmaps
             this.beatmap = beatmap;
         }
 
-        private Beatmap beatmap;
+        private readonly Beatmap beatmap;
         
         protected override Beatmap GetBeatmap() => beatmap;
         protected override Texture GetBackground() => null;

osu.Desktop.VisualTests/Benchmark.cs

@@ -10,7 +10,7 @@ namespace osu.Desktop.VisualTests
 {
     public class Benchmark : OsuGameBase
     {
-        private double timePerTest = 200;
+        private readonly double timePerTest = 200;
 
         [BackgroundDependencyLoader]
         private void load()

osu.Desktop.VisualTests/Tests/TestCaseHitObjects.cs

@@ -21,7 +21,7 @@ namespace osu.Desktop.VisualTests.Tests
 {
     internal class TestCaseHitObjects : TestCase
     {
-        private FramedClock framedClock;
+        private readonly FramedClock framedClock;
 
         private bool auto;
 
@@ -34,7 +34,7 @@ namespace osu.Desktop.VisualTests.Tests
 
         private HitObjectType mode = HitObjectType.Slider;
 
-        private BindableNumber<double> playbackSpeed = new BindableDouble(0.5) { MinValue = 0, MaxValue = 1 };
+        private readonly BindableNumber<double> playbackSpeed = new BindableDouble(0.5) { MinValue = 0, MaxValue = 1 };
         private Container playfieldContainer;
         private Container approachContainer;
 

osu.Desktop.VisualTests/Tests/TestCaseNotificationManager.cs

@@ -95,7 +95,7 @@ namespace osu.Desktop.VisualTests.Tests
             progressingNotifications.Add(n);
         }
 
-        private List<ProgressNotification> progressingNotifications = new List<ProgressNotification>();
+        private readonly List<ProgressNotification> progressingNotifications = new List<ProgressNotification>();
 
         private void sendProgress1()
         {

osu.Desktop/OsuGameDesktop.cs

@@ -17,7 +17,7 @@ namespace osu.Desktop
 {
     internal class OsuGameDesktop : OsuGame
     {
-        private VersionManager versionManager;
+        private readonly VersionManager versionManager;
 
         public OsuGameDesktop(string[] args = null)
             : base(args)

osu.Game.Modes.Catch/Objects/Drawable/DrawableFruit.cs

@@ -12,7 +12,7 @@ namespace osu.Game.Modes.Catch.Objects.Drawable
 {
     internal class DrawableFruit : Sprite
     {
-        private CatchBaseHit h;
+        private readonly CatchBaseHit h;
 
         public DrawableFruit(CatchBaseHit h)
         {

osu.Game.Modes.Osu/Objects/Drawables/DrawableHitCircle.cs

@@ -13,15 +13,15 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
 {
     public class DrawableHitCircle : DrawableOsuHitObject, IDrawableHitObjectWithProxiedApproach
     {
-        private OsuHitObject osuObject;
+        private readonly OsuHitObject osuObject;
 
         public ApproachCircle ApproachCircle;
-        private CirclePiece circle;
-        private RingPiece ring;
-        private FlashPiece flash;
-        private ExplodePiece explode;
-        private NumberPiece number;
-        private GlowPiece glow;
+        private readonly CirclePiece circle;
+        private readonly RingPiece ring;
+        private readonly FlashPiece flash;
+        private readonly ExplodePiece explode;
+        private readonly NumberPiece number;
+        private readonly GlowPiece glow;
 
         public DrawableHitCircle(OsuHitObject h) : base(h)
         {

osu.Game.Modes.Osu/Objects/Drawables/DrawableSlider.cs

@@ -13,18 +13,18 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
 {
     public class DrawableSlider : DrawableOsuHitObject, IDrawableHitObjectWithProxiedApproach
     {
-        private Slider slider;
+        private readonly Slider slider;
 
-        private DrawableHitCircle initialCircle;
+        private readonly DrawableHitCircle initialCircle;
 
-        private List<ISliderProgress> components = new List<ISliderProgress>();
+        private readonly List<ISliderProgress> components = new List<ISliderProgress>();
 
-        private Container<DrawableSliderTick> ticks;
+        private readonly Container<DrawableSliderTick> ticks;
 
-        private SliderBody body;
-        private SliderBall ball;
+        private readonly SliderBody body;
+        private readonly SliderBall ball;
 
-        private SliderBouncer bouncer2;
+        private readonly SliderBouncer bouncer2;
 
         public DrawableSlider(Slider s) : base(s)
         {

osu.Game.Modes.Osu/Objects/Drawables/DrawableSliderTick.cs

@@ -18,7 +18,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
 {
     public class DrawableSliderTick : DrawableOsuHitObject
     {
-        private SliderTick sliderTick;
+        private readonly SliderTick sliderTick;
 
         public double FadeInTime;
         public double FadeOutTime;

osu.Game.Modes.Osu/Objects/Drawables/DrawableSpinner.cs

@@ -15,12 +15,12 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
 {
     public class DrawableSpinner : DrawableOsuHitObject
     {
-        private Spinner spinner;
+        private readonly Spinner spinner;
 
-        private SpinnerDisc disc;
-        private SpinnerBackground background;
-        private Container circleContainer;
-        private DrawableHitCircle circle;
+        private readonly SpinnerDisc disc;
+        private readonly SpinnerBackground background;
+        private readonly Container circleContainer;
+        private readonly DrawableHitCircle circle;
 
         public DrawableSpinner(Spinner s) : base(s)
         {
@@ -108,7 +108,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
 
         private Vector2 scaleToCircle => circle.Scale * circle.DrawWidth / DrawWidth * 0.95f;
 
-        private float spinsPerMinuteNeeded = 100 + 5 * 15; //TODO: read per-map OD and place it on the 5
+        private readonly float spinsPerMinuteNeeded = 100 + 5 * 15; //TODO: read per-map OD and place it on the 5
 
         private float rotationsNeeded => (float)(spinsPerMinuteNeeded * (spinner.EndTime - spinner.StartTime) / 60000f);
 

osu.Game.Modes.Osu/Objects/Drawables/HitExplosion.cs

@@ -17,8 +17,8 @@ namespace osu.Game.Modes.Osu.Objects.Drawables
     public class HitExplosion : FillFlowContainer
     {
         private readonly OsuJudgementInfo judgement;
-        private SpriteText line1;
-        private SpriteText line2;
+        private readonly SpriteText line1;
+        private readonly SpriteText line2;
 
         public HitExplosion(OsuJudgementInfo judgement, OsuHitObject h = null)
         {

osu.Game.Modes.Osu/Objects/Drawables/Pieces/ApproachCircle.cs

@@ -11,7 +11,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
 {
     public class ApproachCircle : Container
     {
-        private Sprite approachCircle;
+        private readonly Sprite approachCircle;
 
         public ApproachCircle()
         {

osu.Game.Modes.Osu/Objects/Drawables/Pieces/CirclePiece.cs

@@ -14,7 +14,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
 {
     public class CirclePiece : Container
     {
-        private Sprite disc;
+        private readonly Sprite disc;
 
 
         public Func<bool> Hit;

osu.Game.Modes.Osu/Objects/Drawables/Pieces/GlowPiece.cs

@@ -11,7 +11,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
 {
     public class GlowPiece : Container
     {
-        private Sprite layer;
+        private readonly Sprite layer;
 
         public GlowPiece()
         {

osu.Game.Modes.Osu/Objects/Drawables/Pieces/NumberPiece.cs

@@ -12,7 +12,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
 {
     public class NumberPiece : Container
     {
-        private SpriteText number;
+        private readonly SpriteText number;
 
         public string Text
         {

osu.Game.Modes.Osu/Objects/Drawables/Pieces/SliderBall.cs

@@ -13,7 +13,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
     public class SliderBall : CircularContainer, ISliderProgress
     {
         private readonly Slider slider;
-        private Box follow;
+        private readonly Box follow;
 
         private const float width = 128;
 

osu.Game.Modes.Osu/Objects/Drawables/Pieces/SliderBody.cs

@@ -18,8 +18,8 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
 {
     public class SliderBody : Container, ISliderProgress
     {
-        private Path path;
-        private BufferedContainer container;
+        private readonly Path path;
+        private readonly BufferedContainer container;
 
         public float PathWidth
         {
@@ -33,7 +33,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
         public double? SnakedStart { get; private set; }
         public double? SnakedEnd { get; private set; }
 
-        private Slider slider;
+        private readonly Slider slider;
         public SliderBody(Slider s)
         {
             slider = s;
@@ -122,7 +122,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
             path.Texture = texture;
         }
 
-        private List<Vector2> currentCurve = new List<Vector2>();
+        private readonly List<Vector2> currentCurve = new List<Vector2>();
         private bool updateSnaking(double p0, double p1)
         {
             if (SnakedStart == p0 && SnakedEnd == p1) return false;

osu.Game.Modes.Osu/Objects/Drawables/Pieces/SliderBouncer.cs

@@ -11,7 +11,7 @@ namespace osu.Game.Modes.Osu.Objects.Drawables.Pieces
     {
         private readonly Slider slider;
         private readonly bool isEnd;
-        private TextAwesome icon;
+        private readonly TextAwesome icon;
 
         public SliderBouncer(Slider slider, bool isEnd)
         {

osu.Game.Modes.Osu/Objects/OsuHitObjectDifficulty.cs

@@ -47,11 +47,11 @@ namespace osu.Game.Modes.Osu.Objects
 
         internal int MaxCombo = 1;
 
-        private float scalingFactor;
+        private readonly float scalingFactor;
         private float lazySliderLength;
 
-        private Vector2 startPosition;
-        private Vector2 endPosition;
+        private readonly Vector2 startPosition;
+        private readonly Vector2 endPosition;
 
         internal OsuHitObjectDifficulty(OsuHitObject baseHitObject)
         {

osu.Game.Modes.Osu/OsuAutoReplay.cs

@@ -20,7 +20,7 @@ namespace osu.Game.Modes.Osu
 
         private const float spin_radius = 50;
 
-        private Beatmap<OsuHitObject> beatmap;
+        private readonly Beatmap<OsuHitObject> beatmap;
 
         public OsuAutoReplay(Beatmap<OsuHitObject> beatmap)
         {
@@ -37,11 +37,11 @@ namespace osu.Game.Modes.Osu
             }
         }
 
-        private static IComparer<LegacyReplayFrame> replayFrameComparer = new LegacyReplayFrameComparer();
+        private static readonly IComparer<LegacyReplayFrame> replay_frame_comparer = new LegacyReplayFrameComparer();
 
         private int findInsertionIndex(LegacyReplayFrame frame)
         {
-            int index = Frames.BinarySearch(frame, replayFrameComparer);
+            int index = Frames.BinarySearch(frame, replay_frame_comparer);
 
             if (index < 0)
             {

osu.Game.Modes.Osu/UI/OsuPlayfield.cs

@@ -17,9 +17,9 @@ namespace osu.Game.Modes.Osu.UI
 {
     public class OsuPlayfield : Playfield<OsuHitObject, OsuJudgementInfo>
     {
-        private Container approachCircles;
-        private Container judgementLayer;
-        private ConnectionRenderer<OsuHitObject> connectionLayer;
+        private readonly Container approachCircles;
+        private readonly Container judgementLayer;
+        private readonly ConnectionRenderer<OsuHitObject> connectionLayer;
 
         public override Vector2 Size
         {

osu.Game.Modes.Taiko/Objects/Drawable/DrawableTaikoHit.cs

@@ -12,7 +12,7 @@ namespace osu.Game.Modes.Taiko.Objects.Drawable
 {
     internal class DrawableTaikoHit : Sprite
     {
-        private TaikoHitObject h;
+        private readonly TaikoHitObject h;
 
         public DrawableTaikoHit(TaikoHitObject h)
         {

osu.Game/Beatmaps/Drawables/BeatmapPanel.cs

@@ -21,12 +21,12 @@ namespace osu.Game.Beatmaps.Drawables
     public class BeatmapPanel : Panel
     {
         public BeatmapInfo Beatmap;
-        private Sprite background;
+        private readonly Sprite background;
 
         public Action<BeatmapPanel> GainedSelection;
         public Action<BeatmapPanel> StartRequested;
-        private Triangles triangles;
-        private StarCounter starCounter;
+        private readonly Triangles triangles;
+        private readonly StarCounter starCounter;
 
         protected override void Selected()
         {

osu.Game/Beatmaps/Drawables/BeatmapSetHeader.cs

@@ -20,11 +20,12 @@ namespace osu.Game.Beatmaps.Drawables
     public class BeatmapSetHeader : Panel
     {
         public Action<BeatmapSetHeader> GainedSelection;
-        private SpriteText title, artist;
+        private readonly SpriteText title;
+        private readonly SpriteText artist;
         private OsuConfigManager config;
         private Bindable<bool> preferUnicode;
-        private WorkingBeatmap beatmap;
-        private FillFlowContainer difficultyIcons;
+        private readonly WorkingBeatmap beatmap;
+        private readonly FillFlowContainer difficultyIcons;
 
         public BeatmapSetHeader(WorkingBeatmap beatmap)
         {

osu.Game/Beatmaps/Drawables/Panel.cs

@@ -18,7 +18,7 @@ namespace osu.Game.Beatmaps.Drawables
 
         public override bool RemoveWhenNotAlive => false;
 
-        private Container nestedContainer;
+        private readonly Container nestedContainer;
 
         protected override Container<Drawable> Content => nestedContainer;
 

osu.Game/Beatmaps/IO/OszArchiveReader.cs

@@ -21,9 +21,9 @@ namespace osu.Game.Beatmaps.IO
             OsuLegacyDecoder.Register();
         }
 
-        private Stream archiveStream;
-        private ZipFile archive;
-        private Beatmap firstMap;
+        private readonly Stream archiveStream;
+        private readonly ZipFile archive;
+        private readonly Beatmap firstMap;
 
         public OszArchiveReader(Stream archiveStream)
         {

osu.Game/Beatmaps/WorkingBeatmap.cs

@@ -42,7 +42,7 @@ namespace osu.Game.Beatmaps
         protected abstract Track GetTrack();
         
         private Beatmap beatmap;
-        private object beatmapLock = new object();
+        private readonly object beatmapLock = new object();
         public Beatmap Beatmap
         {
             get
@@ -54,7 +54,7 @@ namespace osu.Game.Beatmaps
             }
         }
         
-        private object backgroundLock = new object();
+        private readonly object backgroundLock = new object();
         private Texture background;
         public Texture Background
         {
@@ -68,7 +68,7 @@ namespace osu.Game.Beatmaps
         }
 
         private Track track;
-        private object trackLock = new object();
+        private readonly object trackLock = new object();
         public Track Track
         {
             get

osu.Game/Database/BeatmapDatabase.cs

@@ -21,7 +21,7 @@ namespace osu.Game.Database
     public class BeatmapDatabase
     {
         private SQLiteConnection connection { get; }
-        private Storage storage;
+        private readonly Storage storage;
         public event Action<BeatmapSetInfo> BeatmapSetAdded;
         public event Action<BeatmapSetInfo> BeatmapSetRemoved;
 

osu.Game/Graphics/Backgrounds/Background.cs

@@ -14,7 +14,7 @@ namespace osu.Game.Graphics.Backgrounds
     {
         public Sprite Sprite;
 
-        private string textureName;
+        private readonly string textureName;
 
         public Background(string textureName = @"")
         {

osu.Game/Graphics/Containers/ParallaxContainer.cs

@@ -31,7 +31,7 @@ namespace osu.Game.Graphics.Containers
             });
         }
 
-        private Container content;
+        private readonly Container content;
         private InputManager input;
 
         protected override Container<Drawable> Content => content;

osu.Game/Graphics/Cursor/CursorTrail.cs

@@ -31,10 +31,10 @@ namespace osu.Game.Graphics.Cursor
 
         private float time;
 
-        private TrailDrawNodeSharedData trailDrawNodeSharedData = new TrailDrawNodeSharedData();
+        private readonly TrailDrawNodeSharedData trailDrawNodeSharedData = new TrailDrawNodeSharedData();
         private const int max_sprites = 2048;
 
-        private TrailPart[] parts = new TrailPart[max_sprites];
+        private readonly TrailPart[] parts = new TrailPart[max_sprites];
 
         private Vector2? lastPosition;
 
@@ -163,7 +163,7 @@ namespace osu.Game.Graphics.Cursor
             public float Time;
             public TrailDrawNodeSharedData Shared;
 
-            public TrailPart[] Parts = new TrailPart[max_sprites];
+            public readonly TrailPart[] Parts = new TrailPart[max_sprites];
             public Vector2 Size;
 
             public TrailDrawNode()

osu.Game/Graphics/UserInterface/DialogButton.cs

@@ -81,9 +81,14 @@ namespace osu.Game.Graphics.UserInterface
 
         public SampleChannel SampleClick, SampleHover;
 
-        private Container backgroundContainer, colourContainer, glowContainer;
-        private Box leftGlow, centerGlow, rightGlow, background;
-        private SpriteText spriteText;
+        private readonly Container backgroundContainer;
+        private readonly Container colourContainer;
+        private readonly Container glowContainer;
+        private readonly Box leftGlow;
+        private readonly Box centerGlow;
+        private readonly Box rightGlow;
+        private readonly Box background;
+        private readonly SpriteText spriteText;
         private Vector2 hoverSpacing => new Vector2(3f, 0f);
 
         private bool didClick; // Used for making sure that the OnMouseDown animation can call instead of OnHoverLost's when clicking

osu.Game/Graphics/UserInterface/Nub.cs

@@ -18,7 +18,7 @@ namespace osu.Game.Graphics.UserInterface
         public const float COLLAPSED_SIZE = 20;
         public const float EXPANDED_SIZE = 40;
 
-        private Box fill;
+        private readonly Box fill;
 
         private const float border_width = 3;
         private Color4 glowingColour, idleColour;

osu.Game/Graphics/UserInterface/OsuCheckbox.cs

@@ -64,8 +64,8 @@ namespace osu.Game.Graphics.UserInterface
             }
         }
 
-        private Nub nub;
-        private SpriteText labelSpriteText;
+        private readonly Nub nub;
+        private readonly SpriteText labelSpriteText;
         private SampleChannel sampleChecked;
         private SampleChannel sampleUnchecked;
 

osu.Game/Graphics/UserInterface/OsuDropdown.cs

@@ -85,7 +85,7 @@ namespace osu.Game.Graphics.UserInterface
 
             private Color4? accentColour;
 
-            private TextAwesome chevron;
+            private readonly TextAwesome chevron;
 
             protected override void FormatForeground(bool hover = false)
             {
@@ -116,7 +116,7 @@ namespace osu.Game.Graphics.UserInterface
 
         protected class OsuDropdownHeader : DropdownHeader
         {
-            private SpriteText label;
+            private readonly SpriteText label;
             protected override string Label
             {
                 get { return label.Text; }

osu.Game/Graphics/UserInterface/OsuPasswordTextBox.cs

@@ -18,7 +18,7 @@ namespace osu.Game.Graphics.UserInterface
 
         public class PasswordMaskChar : Container
         {
-            private CircularContainer circle;
+            private readonly CircularContainer circle;
 
             public PasswordMaskChar(float size)
             {

osu.Game/Graphics/UserInterface/OsuSliderBar.cs

@@ -19,8 +19,9 @@ namespace osu.Game.Graphics.UserInterface
         private SampleChannel sample;
         private double lastSampleTime;
 
-        private Nub nub;
-        private Box leftBox, rightBox;
+        private readonly Nub nub;
+        private readonly Box leftBox;
+        private readonly Box rightBox;
 
         public OsuSliderBar()
         {

osu.Game/Graphics/UserInterface/OsuTabControl.cs

@@ -59,8 +59,8 @@ namespace osu.Game.Graphics.UserInterface
 
         private class OsuTabItem : TabItem<T>
         {
-            private SpriteText text;
-            private Box box;
+            private readonly SpriteText text;
+            private readonly Box box;
 
             private Color4? accentColour;
             public Color4 AccentColour

osu.Game/Graphics/UserInterface/StarCounter.cs

@@ -147,7 +147,7 @@ namespace osu.Game.Graphics.UserInterface
 
         private class Star : Container
         {
-            public TextAwesome Icon;
+            public readonly TextAwesome Icon;
             public Star()
             {
                 Size = new Vector2(star_size);

osu.Game/Graphics/UserInterface/TwoLayerButton.cs

@@ -16,7 +16,7 @@ namespace osu.Game.Graphics.UserInterface
 {
     public class TwoLayerButton : ClickableContainer
     {
-        private TextAwesome icon;
+        private readonly TextAwesome icon;
 
         public Box IconLayer;
         public Box TextLayer;
@@ -29,11 +29,11 @@ namespace osu.Game.Graphics.UserInterface
         public static readonly Vector2 SIZE_EXTENDED = new Vector2(140, 50);
         public static readonly Vector2 SIZE_RETRACTED = new Vector2(100, 50);
         public SampleChannel ActivationSound;
-        private SpriteText text;
+        private readonly SpriteText text;
 
         public Color4 HoverColour;
-        private Container c1;
-        private Container c2;
+        private readonly Container c1;
+        private readonly Container c2;
 
         public Color4 BackgroundColour
         {

osu.Game/Graphics/UserInterface/Volume/VolumeControl.cs

@@ -15,7 +15,7 @@ namespace osu.Game.Graphics.UserInterface.Volume
 {
     internal class VolumeControl : OverlayContainer
     {
-        private VolumeMeter volumeMeterMaster;
+        private readonly VolumeMeter volumeMeterMaster;
 
         protected override bool HideOnEscape => false;
 
@@ -89,8 +89,8 @@ namespace osu.Game.Graphics.UserInterface.Volume
 
         private ScheduledDelegate popOutDelegate;
 
-        private VolumeMeter volumeMeterEffect;
-        private VolumeMeter volumeMeterMusic;
+        private readonly VolumeMeter volumeMeterEffect;
+        private readonly VolumeMeter volumeMeterMusic;
 
         protected override void PopIn()
         {

osu.Game/Graphics/UserInterface/Volume/VolumeMeter.cs

@@ -15,7 +15,7 @@ namespace osu.Game.Graphics.UserInterface.Volume
 {
     internal class VolumeMeter : Container
     {
-        private Box meterFill;
+        private readonly Box meterFill;
         public BindableDouble Bindable { get; } = new BindableDouble();
 
         public VolumeMeter(string meterName)

osu.Game/IO/Legacy/SerializationReader.cs

@@ -18,7 +18,7 @@ namespace osu.Game.IO.Legacy
     /// handle null strings and simplify use with ISerializable. </summary>
     public class SerializationReader : BinaryReader
     {
-        private Stream stream;
+        private readonly Stream stream;
 
         public SerializationReader(Stream s)
             : base(s, Encoding.UTF8)

osu.Game/IPC/BeatmapIPCChannel.cs

@@ -10,7 +10,7 @@ namespace osu.Game.IPC
 {
     public class BeatmapIPCChannel : IpcChannel<BeatmapImportMessage>
     {
-        private BeatmapDatabase beatmaps;
+        private readonly BeatmapDatabase beatmaps;
 
         public BeatmapIPCChannel(IIpcHost host, BeatmapDatabase beatmaps = null)
             : base(host)

osu.Game/IPC/ScoreIPCChannel.cs

@@ -10,7 +10,7 @@ namespace osu.Game.IPC
 {
     public class ScoreIPCChannel : IpcChannel<ScoreImportMessage>
     {
-        private ScoreDatabase scores;
+        private readonly ScoreDatabase scores;
 
         public ScoreIPCChannel(IIpcHost host, ScoreDatabase scores = null)
             : base(host)

osu.Game/Modes/Objects/BezierApproximator.cs

@@ -8,10 +8,10 @@ namespace osu.Game.Modes.Objects
 {
     public class BezierApproximator
     {
-        private int count;
-        private List<Vector2> controlPoints;
-        private Vector2[] subdivisionBuffer1;
-        private Vector2[] subdivisionBuffer2;
+        private readonly int count;
+        private readonly List<Vector2> controlPoints;
+        private readonly Vector2[] subdivisionBuffer1;
+        private readonly Vector2[] subdivisionBuffer2;
 
         private const float tolerance = 0.25f;
         private const float tolerance_sq = tolerance * tolerance;

osu.Game/Modes/Objects/CircularArcApproximator.cs

@@ -10,9 +10,9 @@ namespace osu.Game.Modes.Objects
 {
     public class CircularArcApproximator
     {
-        private Vector2 a;
-        private Vector2 b;
-        private Vector2 c;
+        private readonly Vector2 a;
+        private readonly Vector2 b;
+        private readonly Vector2 c;
 
         private int amountPoints;
 

osu.Game/Modes/Objects/SliderCurve.cs

@@ -19,8 +19,8 @@ namespace osu.Game.Modes.Objects
 
         public Vector2 Offset;
 
-        private List<Vector2> calculatedPath = new List<Vector2>();
-        private List<double> cumulativeLength = new List<double>();
+        private readonly List<Vector2> calculatedPath = new List<Vector2>();
+        private readonly List<double> cumulativeLength = new List<double>();
 
         private List<Vector2> calculateSubpath(List<Vector2> subControlPoints)
         {

osu.Game/Modes/Ruleset.cs

@@ -21,9 +21,9 @@ namespace osu.Game.Modes
 
     public abstract class Ruleset
     {
-        private static ConcurrentDictionary<PlayMode, Type> availableRulesets = new ConcurrentDictionary<PlayMode, Type>();
+        private static readonly ConcurrentDictionary<PlayMode, Type> available_rulesets = new ConcurrentDictionary<PlayMode, Type>();
 
-        public static IEnumerable<PlayMode> PlayModes => availableRulesets.Keys;
+        public static IEnumerable<PlayMode> PlayModes => available_rulesets.Keys;
 
         public virtual IEnumerable<BeatmapStatistic> GetBeatmapStatistics(WorkingBeatmap beatmap) => new BeatmapStatistic[] { };
 
@@ -35,7 +35,7 @@ namespace osu.Game.Modes
 
         public abstract ScoreProcessor CreateScoreProcessor();
 
-        public static void Register(Ruleset ruleset) => availableRulesets.TryAdd(ruleset.PlayMode, ruleset.GetType());
+        public static void Register(Ruleset ruleset) => available_rulesets.TryAdd(ruleset.PlayMode, ruleset.GetType());
 
         protected abstract PlayMode PlayMode { get; }
 
@@ -49,7 +49,7 @@ namespace osu.Game.Modes
         {
             Type type;
 
-            if (!availableRulesets.TryGetValue(mode, out type))
+            if (!available_rulesets.TryGetValue(mode, out type))
                 return null;
 
             return Activator.CreateInstance(type) as Ruleset;

osu.Game/Modes/UI/HitRenderer.cs

@@ -155,7 +155,7 @@ namespace osu.Game.Modes.UI
         /// </summary>
         protected Playfield<TObject, TJudgement> Playfield;
 
-        private Container content;
+        private readonly Container content;
 
         protected HitRenderer(WorkingBeatmap beatmap)
             : base(beatmap)

osu.Game/Modes/UI/ModIcon.cs

@@ -10,7 +10,8 @@ namespace osu.Game.Modes.UI
 {
     public class ModIcon : Container
     {
-        private TextAwesome modIcon, background;
+        private readonly TextAwesome modIcon;
+        private readonly TextAwesome background;
 
         private float iconSize = 80;
         public float IconSize

osu.Game/Modes/UI/Playfield.cs

@@ -23,7 +23,7 @@ namespace osu.Game.Modes.UI
         internal Container<Drawable> ScaledContent;
 
         protected override Container<Drawable> Content => content;
-        private Container<Drawable> content;
+        private readonly Container<Drawable> content;
 
         /// <summary>
         /// A container for keeping track of DrawableHitObjects.

osu.Game/Modes/UI/StandardHealthDisplay.cs

@@ -15,7 +15,7 @@ namespace osu.Game.Modes.UI
 {
     public class StandardHealthDisplay : HealthDisplay
     {
-        private Container fill;
+        private readonly Container fill;
 
         public StandardHealthDisplay()
         {

osu.Game/Online/API/APIAccess.cs

@@ -17,7 +17,7 @@ namespace osu.Game.Online.API
 {
     public class APIAccess : IUpdateable
     {
-        private OAuth authentication;
+        private readonly OAuth authentication;
 
         public string Endpoint = @"https://new.ppy.sh";
         private const string client_id = @"5";
@@ -44,9 +44,9 @@ namespace osu.Game.Online.API
         protected bool HasLogin => Token != null || !string.IsNullOrEmpty(Username) && !string.IsNullOrEmpty(Password);
 
         // ReSharper disable once PrivateFieldCanBeConvertedToLocalVariable (should dispose of this or at very least keep a reference).
-        private Thread thread;
+        private readonly Thread thread;
 
-        private Logger log;
+        private readonly Logger log;
 
         public APIAccess()
         {
@@ -57,7 +57,7 @@ namespace osu.Game.Online.API
             thread.Start();
         }
 
-        private List<IOnlineComponent> components = new List<IOnlineComponent>();
+        private readonly List<IOnlineComponent> components = new List<IOnlineComponent>();
 
         public void Register(IOnlineComponent component)
         {

osu.Game/Online/API/Requests/GetMessagesRequest.cs

@@ -9,7 +9,7 @@ namespace osu.Game.Online.API.Requests
 {
     public class GetMessagesRequest : APIRequest<List<Message>>
     {
-        private List<Channel> channels;
+        private readonly List<Channel> channels;
         private long? since;
 
         public GetMessagesRequest(List<Channel> channels, long? sinceId)

osu.Game/Online/Chat/Drawables/DrawableChannel.cs

@@ -14,8 +14,8 @@ namespace osu.Game.Online.Chat.Drawables
     public class DrawableChannel : Container
     {
         private readonly Channel channel;
-        private FillFlowContainer flow;
-        private ScrollContainer scroll;
+        private readonly FillFlowContainer flow;
+        private readonly ScrollContainer scroll;
 
         public DrawableChannel(Channel channel)
         {

osu.Game/OsuGame.cs

@@ -60,7 +60,7 @@ namespace osu.Game
 
         public Bindable<PlayMode> PlayMode;
 
-        private string[] args;
+        private readonly string[] args;
 
         private OptionsOverlay options;
 

osu.Game/Overlays/ChatOverlay.cs

@@ -31,11 +31,11 @@ namespace osu.Game.Overlays
 
         private ScheduledDelegate messageRequest;
 
-        private Container content;
+        private readonly Container content;
 
         protected override Container<Drawable> Content => content;
 
-        private FocusedTextBox inputTextBox;
+        private readonly FocusedTextBox inputTextBox;
 
         private APIAccess api;
 

osu.Game/Overlays/Dialog/PopupDialog.cs

@@ -27,10 +27,12 @@ namespace osu.Game.Overlays.Dialog
         private readonly Vector2 ringMinifiedSize = new Vector2(20f);
         private readonly Vector2 buttonsEnterSpacing = new Vector2(0f, 50f);
 
-        private Container content, ring;
-        private FillFlowContainer<PopupDialogButton> buttonsContainer;
-        private TextAwesome iconText;
-        private SpriteText header, body;
+        private readonly Container content;
+        private readonly Container ring;
+        private readonly FillFlowContainer<PopupDialogButton> buttonsContainer;
+        private readonly TextAwesome iconText;
+        private readonly SpriteText header;
+        private readonly SpriteText body;
 
         public FontAwesome Icon
         {

osu.Game/Overlays/DialogOverlay.cs

@@ -13,7 +13,7 @@ namespace osu.Game.Overlays
 {
     public class DialogOverlay : FocusedOverlayContainer
     {
-        private Container dialogContainer;
+        private readonly Container dialogContainer;
         private PopupDialog currentDialog;
 
         public void Push(PopupDialog dialog)

osu.Game/Overlays/DragBar.cs

@@ -11,7 +11,7 @@ namespace osu.Game.Overlays
 {
     public class DragBar : Container
     {
-        private Box fill;
+        private readonly Box fill;
 
         public Action<float> SeekRequested;
         private bool isDragging;

osu.Game/Overlays/Mods/ModButton.cs

@@ -23,8 +23,8 @@ namespace osu.Game.Overlays.Mods
     public class ModButton : FillFlowContainer
     {
         private ModIcon foregroundIcon { get; set; }
-        private SpriteText text;
-        private Container<ModIcon> iconsContainer;
+        private readonly SpriteText text;
+        private readonly Container<ModIcon> iconsContainer;
         private SampleChannel sampleOn, sampleOff;
 
         public Action<Mod> Action; // Passed the selected mod or null if none

osu.Game/Overlays/Mods/ModSection.cs

@@ -16,7 +16,7 @@ namespace osu.Game.Overlays.Mods
 {
     public abstract class ModSection : Container
     {
-        private OsuSpriteText headerLabel;
+        private readonly OsuSpriteText headerLabel;
 
         public FillFlowContainer<ModButton> ButtonsContainer { get; }
 

osu.Game/Overlays/Mods/ModSelectOverlay.cs

@@ -30,10 +30,11 @@ namespace osu.Game.Overlays.Mods
 
         private Color4 lowMultiplierColour, highMultiplierColour;
 
-        private OsuSpriteText rankedLabel, multiplierLabel;
-        private FillFlowContainer rankedMultiplerContainer;
+        private readonly OsuSpriteText rankedLabel;
+        private readonly OsuSpriteText multiplierLabel;
+        private readonly FillFlowContainer rankedMultiplerContainer;
 
-        private FillFlowContainer<ModSection> modSectionsContainer;
+        private readonly FillFlowContainer<ModSection> modSectionsContainer;
 
         public readonly Bindable<IEnumerable<Mod>> SelectedMods = new Bindable<IEnumerable<Mod>>();
 

osu.Game/Overlays/MusicController.cs

@@ -35,7 +35,7 @@ namespace osu.Game.Overlays
         private SpriteText title, artist;
 
         private List<BeatmapSetInfo> playList;
-        private List<BeatmapInfo> playHistory = new List<BeatmapInfo>();
+        private readonly List<BeatmapInfo> playHistory = new List<BeatmapInfo>();
         private int playListIndex;
         private int playHistoryIndex = -1;
 
@@ -415,8 +415,8 @@ namespace osu.Game.Overlays
 
         private class MusicControllerBackground : BufferedContainer
         {
-            private Sprite sprite;
-            private WorkingBeatmap beatmap;
+            private readonly Sprite sprite;
+            private readonly WorkingBeatmap beatmap;
 
             public MusicControllerBackground(WorkingBeatmap beatmap = null)
             {

osu.Game/Overlays/Notifications/Notification.cs

@@ -35,9 +35,9 @@ namespace osu.Game.Overlays.Notifications
         public virtual bool DisplayOnTop => true;
 
         protected NotificationLight Light;
-        private CloseButton closeButton;
+        private readonly CloseButton closeButton;
         protected Container IconContent;
-        private Container content;
+        private readonly Container content;
 
         protected override Container<Drawable> Content => content;
 

osu.Game/Overlays/Notifications/NotificationSection.cs

@@ -135,7 +135,7 @@ namespace osu.Game.Overlays.Notifications
 
         private class ClearAllButton : ClickableContainer
         {
-            private OsuSpriteText text;
+            private readonly OsuSpriteText text;
 
             public ClearAllButton()
             {

osu.Game/Overlays/Notifications/ProgressNotification.cs

@@ -104,12 +104,12 @@ namespace osu.Game.Overlays.Notifications
 
         public override bool DisplayOnTop => false;
 
-        private ProgressBar progressBar;
+        private readonly ProgressBar progressBar;
         private Color4 colourQueued;
         private Color4 colourActive;
         private Color4 colourCancelled;
 
-        private SpriteText textDrawable;
+        private readonly SpriteText textDrawable;
 
         public ProgressNotification()
         {

osu.Game/Overlays/Notifications/SimpleNotification.cs

@@ -34,8 +34,8 @@ namespace osu.Game.Overlays.Notifications
             }
         }
 
-        private SpriteText textDrawable;
-        private TextAwesome iconDrawable;
+        private readonly SpriteText textDrawable;
+        private readonly TextAwesome iconDrawable;
 
         protected Box IconBackgound;
 

osu.Game/Overlays/Options/OptionDropdown.cs

@@ -15,8 +15,8 @@ namespace osu.Game.Overlays.Options
 {
     public class OptionDropdown<T> : FillFlowContainer
     {
-        private Dropdown<T> dropdown;
-        private SpriteText text;
+        private readonly Dropdown<T> dropdown;
+        private readonly SpriteText text;
 
         public string LabelText
         {

osu.Game/Overlays/Options/OptionSlider.cs

@@ -14,8 +14,8 @@ namespace osu.Game.Overlays.Options
 {
     public class OptionSlider<T> : FillFlowContainer where T : struct
     {
-        private SliderBar<T> slider;
-        private SpriteText text;
+        private readonly SliderBar<T> slider;
+        private readonly SpriteText text;
 
         public string LabelText
         {

osu.Game/Overlays/Options/OptionsSection.cs

@@ -21,7 +21,7 @@ namespace osu.Game.Overlays.Options
         public abstract FontAwesome Icon { get; }
         public abstract string Header { get; }
 
-        private SpriteText headerLabel;
+        private readonly SpriteText headerLabel;
 
         protected OptionsSection()
         {

osu.Game/Overlays/Options/OptionsSubsection.cs

@@ -13,7 +13,7 @@ namespace osu.Game.Overlays.Options
     {
         protected override Container<Drawable> Content => content;
 
-        private Container<Drawable> content;
+        private readonly Container<Drawable> content;
 
         protected abstract string Header { get; }
 

osu.Game/Overlays/Options/Sidebar.cs

@@ -15,7 +15,7 @@ namespace osu.Game.Overlays.Options
 {
     public class Sidebar : Container
     {
-        private FillFlowContainer content;
+        private readonly FillFlowContainer content;
         internal const float DEFAULT_WIDTH = ToolbarButton.WIDTH;
         internal const int EXPANDED_WIDTH = 200;
         protected override Container<Drawable> Content => content;

osu.Game/Overlays/Options/SidebarButton.cs

@@ -16,11 +16,11 @@ namespace osu.Game.Overlays.Options
 {
     public class SidebarButton : Container
     {
-        private TextAwesome drawableIcon;
-        private SpriteText headerText;
-        private Box backgroundBox;
-        private Box selectionIndicator;
-        private Container text;
+        private readonly TextAwesome drawableIcon;
+        private readonly SpriteText headerText;
+        private readonly Box backgroundBox;
+        private readonly Box selectionIndicator;
+        private readonly Container text;
         public Action Action;
 
         private OptionsSection section;

osu.Game/Overlays/Toolbar/Toolbar.cs

@@ -23,8 +23,8 @@ namespace osu.Game.Overlays.Toolbar
         public Action OnHome;
         public Action<PlayMode> OnPlayModeChange;
 
-        private ToolbarModeSelector modeSelector;
-        private ToolbarUserArea userArea;
+        private readonly ToolbarModeSelector modeSelector;
+        private readonly ToolbarUserArea userArea;
 
         protected override bool HideOnEscape => false;
 
@@ -90,8 +90,8 @@ namespace osu.Game.Overlays.Toolbar
 
         public class ToolbarBackground : Container
         {
-            private Box solidBackground;
-            private Box gradientBackground;
+            private readonly Box solidBackground;
+            private readonly Box gradientBackground;
 
             public ToolbarBackground()
             {

osu.Game/Overlays/Toolbar/ToolbarButton.cs

@@ -63,9 +63,9 @@ namespace osu.Game.Overlays.Toolbar
         protected TextAwesome DrawableIcon;
         protected SpriteText DrawableText;
         protected Box HoverBackground;
-        private FillFlowContainer tooltipContainer;
-        private SpriteText tooltip1;
-        private SpriteText tooltip2;
+        private readonly FillFlowContainer tooltipContainer;
+        private readonly SpriteText tooltip1;
+        private readonly SpriteText tooltip2;
         protected FillFlowContainer Flow;
         private SampleChannel sampleClick;
 

osu.Game/Overlays/Toolbar/ToolbarModeSelector.cs

@@ -19,8 +19,8 @@ namespace osu.Game.Overlays.Toolbar
     {
         private const float padding = 10;
 
-        private FillFlowContainer modeButtons;
-        private Drawable modeButtonLine;
+        private readonly FillFlowContainer modeButtons;
+        private readonly Drawable modeButtonLine;
         private ToolbarModeButton activeButton;
 
         public Action<PlayMode> OnPlayModeChange;

osu.Game/Overlays/Toolbar/ToolbarOverlayToggleButton.cs

@@ -11,7 +11,7 @@ namespace osu.Game.Overlays.Toolbar
 {
     internal class ToolbarOverlayToggleButton : ToolbarButton
     {
-        private Box stateBackground;
+        private readonly Box stateBackground;
 
         private OverlayContainer stateContainer;
 

osu.Game/Overlays/Toolbar/ToolbarUserArea.cs

@@ -11,7 +11,7 @@ namespace osu.Game.Overlays.Toolbar
     internal class ToolbarUserArea : Container
     {
         public LoginOverlay LoginOverlay;
-        private ToolbarUserButton button;
+        private readonly ToolbarUserButton button;
 
         public override RectangleF BoundingBox => button.BoundingBox;
 

osu.Game/Overlays/Toolbar/ToolbarUserButton.cs

@@ -14,7 +14,7 @@ namespace osu.Game.Overlays.Toolbar
 {
     internal class ToolbarUserButton : ToolbarButton, IOnlineComponent
     {
-        private Avatar avatar;
+        private readonly Avatar avatar;
 
         public ToolbarUserButton()
         {

osu.Game/Overlays/WaveOverlayContainer.cs

@@ -20,9 +20,12 @@ namespace osu.Game.Overlays
         private const EasingTypes easing_show = EasingTypes.OutSine;
         private const EasingTypes easing_hide = EasingTypes.InSine;
 
-        private Wave firstWave, secondWave, thirdWave, fourthWave;
+        private readonly Wave firstWave;
+        private readonly Wave secondWave;
+        private readonly Wave thirdWave;
+        private readonly Wave fourthWave;
 
-        private Container<Wave> wavesContainer;
+        private readonly Container<Wave> wavesContainer;
 
         private readonly Container contentContainer;
 

osu.Game/Screens/Backgrounds/BackgroundScreenBeatmap.cs

@@ -72,7 +72,7 @@ namespace osu.Game.Screens.Backgrounds
 
         private class BeatmapBackground : Background
         {
-            private WorkingBeatmap beatmap;
+            private readonly WorkingBeatmap beatmap;
 
             public BeatmapBackground(WorkingBeatmap beatmap)
             {

osu.Game/Screens/GameScreenWhiteBox.cs

@@ -19,14 +19,14 @@ namespace osu.Game.Screens
 {
     public class ScreenWhiteBox : OsuScreen
     {
-        private BackButton popButton;
+        private readonly BackButton popButton;
 
         private const double transition_time = 1000;
 
         protected virtual IEnumerable<Type> PossibleChildren => null;
 
-        private Container textContainer;
-        private Box box;
+        private readonly Container textContainer;
+        private readonly Box box;
 
         protected override BackgroundScreen CreateBackground() => new BackgroundScreenCustom(@"Backgrounds/bg2");
 

osu.Game/Screens/Menu/Button.cs

@@ -26,13 +26,13 @@ namespace osu.Game.Screens.Menu
     /// </summary>
     public class Button : Container, IStateful<ButtonState>
     {
-        private Container iconText;
-        private Container box;
-        private Box boxHoverLayer;
-        private TextAwesome icon;
-        private string internalName;
-        private Action clickAction;
-        private Key triggerKey;
+        private readonly Container iconText;
+        private readonly Container box;
+        private readonly Box boxHoverLayer;
+        private readonly TextAwesome icon;
+        private readonly string internalName;
+        private readonly Action clickAction;
+        private readonly Key triggerKey;
         private SampleChannel sampleClick;
 
         protected override bool InternalContains(Vector2 screenSpacePos) => box.Contains(screenSpacePos);

osu.Game/Screens/Menu/ButtonSystem.cs

@@ -32,7 +32,7 @@ namespace osu.Game.Screens.Menu
 
         private Toolbar toolbar;
 
-        private FlowContainerWithOrigin buttonFlow;
+        private readonly FlowContainerWithOrigin buttonFlow;
 
         //todo: make these non-internal somehow.
         internal const float BUTTON_AREA_HEIGHT = 100;
@@ -41,16 +41,16 @@ namespace osu.Game.Screens.Menu
 
         public const int EXIT_DELAY = 3000;
 
-        private OsuLogo osuLogo;
-        private Drawable iconFacade;
-        private Container buttonArea;
-        private Box buttonAreaBackground;
+        private readonly OsuLogo osuLogo;
+        private readonly Drawable iconFacade;
+        private readonly Container buttonArea;
+        private readonly Box buttonAreaBackground;
 
-        private Button backButton;
-        private Button settingsButton;
+        private readonly Button backButton;
+        private readonly Button settingsButton;
 
-        private List<Button> buttonsTopLevel = new List<Button>();
-        private List<Button> buttonsPlay = new List<Button>();
+        private readonly List<Button> buttonsTopLevel = new List<Button>();
+        private readonly List<Button> buttonsPlay = new List<Button>();
 
         public ButtonSystem()
         {

osu.Game/Screens/Menu/Disclaimer.cs

@@ -16,7 +16,7 @@ namespace osu.Game.Screens.Menu
     internal class Disclaimer : OsuScreen
     {
         private Intro intro;
-        private TextAwesome icon;
+        private readonly TextAwesome icon;
         private Color4 iconColour;
 
         internal override bool ShowOverlays => false;

osu.Game/Screens/Menu/Intro.cs

@@ -16,7 +16,7 @@ namespace osu.Game.Screens.Menu
 {
     public class Intro : OsuScreen
     {
-        private OsuLogo logo;
+        private readonly OsuLogo logo;
 
         /// <summary>
         /// Whether we have loaded the menu previously.

osu.Game/Screens/Menu/MainMenu.cs

@@ -22,11 +22,11 @@ namespace osu.Game.Screens.Menu
 {
     public class MainMenu : OsuScreen
     {
-        private ButtonSystem buttons;
+        private readonly ButtonSystem buttons;
 
         internal override bool ShowOverlays => buttons.State != MenuState.Initial;
 
-        private BackgroundScreen background;
+        private readonly BackgroundScreen background;
         private Screen songSelect;
 
         protected override BackgroundScreen CreateBackground() => background;

osu.Game/Screens/Menu/OsuLogo.cs

@@ -25,22 +25,22 @@ namespace osu.Game.Screens.Menu
     {
         public Color4 OsuPink = OsuColour.FromHex(@"e967a1");
 
-        private Sprite logo;
-        private CircularContainer logoContainer;
-        private Container logoBounceContainer;
-        private Container logoHoverContainer;
+        private readonly Sprite logo;
+        private readonly CircularContainer logoContainer;
+        private readonly Container logoBounceContainer;
+        private readonly Container logoHoverContainer;
 
         private SampleChannel sampleClick;
 
-        private Container colourAndTriangles;
+        private readonly Container colourAndTriangles;
 
         public Action Action;
 
         public float SizeForFlow => logo == null ? 0 : logo.DrawSize.X * logo.Scale.X * logoBounceContainer.Scale.X * logoHoverContainer.Scale.X * 0.78f;
 
-        private Sprite ripple;
+        private readonly Sprite ripple;
 
-        private Container rippleContainer;
+        private readonly Container rippleContainer;
 
         public bool Triangles
         {
@@ -62,7 +62,7 @@ namespace osu.Game.Screens.Menu
         }
 
         public bool Interactive = true;
-        private Box flashLayer;
+        private readonly Box flashLayer;
 
         public OsuLogo()
         {

osu.Game/Screens/Play/KeyCounterCollection.cs

@@ -106,7 +106,7 @@ namespace osu.Game.Screens.Play
 
         public class Receptor : Drawable
         {
-            private KeyCounterCollection target;
+            private readonly KeyCounterCollection target;
 
             public Receptor(KeyCounterCollection target)
             {

osu.Game/Screens/Play/Pause/PauseProgressBar.cs

@@ -13,10 +13,10 @@ namespace osu.Game.Screens.Play.Pause
 {
     public class PauseProgressBar : Container
     {
-        private Color4 fillColour = new Color4(221, 255, 255, 255);
-        private Color4 glowColour = new Color4(221, 255, 255, 150);
+        private readonly Color4 fillColour = new Color4(221, 255, 255, 255);
+        private readonly Color4 glowColour = new Color4(221, 255, 255, 150);
 
-        private Container fill;
+        private readonly Container fill;
         private WorkingBeatmap current;
 
         [BackgroundDependencyLoader]

osu.Game/Screens/Play/Player.cs

@@ -42,7 +42,7 @@ namespace osu.Game.Screens.Play
 
         public int RestartCount;
 
-        private double pauseCooldown = 1000;
+        private readonly double pauseCooldown = 1000;
         private double lastPauseActionTime;
 
         private bool canPause => Time.Current >= lastPauseActionTime + pauseCooldown;

osu.Game/Screens/Play/PlayerInputManager.cs

@@ -9,7 +9,7 @@ namespace osu.Game.Screens.Play
 {
     public class PlayerInputManager : PassThroughInputManager
     {
-        private ManualClock clock = new ManualClock();
+        private readonly ManualClock clock = new ManualClock();
         private IFrameBasedClock parentClock;
 
         private ReplayInputHandler replayInputHandler;

osu.Game/Screens/Play/PlayerLoader.cs

@@ -21,7 +21,7 @@ namespace osu.Game.Screens.Play
     public class PlayerLoader : OsuScreen
     {
         private readonly Player player;
-        private OsuLogo logo;
+        private readonly OsuLogo logo;
         private BeatmapMetadataDisplay info;
 
         protected override BackgroundScreen CreateBackground() => new BackgroundScreenBeatmap(Beatmap);

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -60,18 +60,18 @@ namespace osu.Game.Screens.Select
             }
         }
 
-        private List<float> yPositions = new List<float>();
+        private readonly List<float> yPositions = new List<float>();
 
         /// <summary>
         /// Required for now unfortunately.
         /// </summary>
         private BeatmapDatabase database;
 
-        private Container<Panel> scrollableContent;
+        private readonly Container<Panel> scrollableContent;
 
-        private List<BeatmapGroup> groups = new List<BeatmapGroup>();
+        private readonly List<BeatmapGroup> groups = new List<BeatmapGroup>();
 
-        private List<Panel> panels = new List<Panel>();
+        private readonly List<Panel> panels = new List<Panel>();
 
         private BeatmapGroup selectedGroup;
 

osu.Game/Screens/Select/FilterControl.cs

@@ -24,9 +24,9 @@ namespace osu.Game.Screens.Select
     {
         public Action<FilterCriteria> FilterChanged;
 
-        private OsuTabControl<SortMode> sortTabs;
+        private readonly OsuTabControl<SortMode> sortTabs;
 
-        private TabControl<GroupMode> groupTabs;
+        private readonly TabControl<GroupMode> groupTabs;
 
         private SortMode sort = SortMode.Title;
         public SortMode Sort
@@ -66,7 +66,7 @@ namespace osu.Game.Screens.Select
 
         public Action Exit;
 
-        private SearchTextBox searchTextBox;
+        private readonly SearchTextBox searchTextBox;
 
         protected override bool InternalContains(Vector2 screenSpacePos) => base.InternalContains(screenSpacePos) || groupTabs.Contains(screenSpacePos) || sortTabs.Contains(screenSpacePos);
 

osu.Game/Screens/Select/Footer.cs

@@ -17,7 +17,7 @@ namespace osu.Game.Screens.Select
 {
     public class Footer : Container
     {
-        private Box modeLight;
+        private readonly Box modeLight;
 
         private const float play_song_select_button_width = 100;
         private const float play_song_select_button_height = 50;
@@ -29,7 +29,7 @@ namespace osu.Game.Screens.Select
         public Action OnBack;
         public Action OnStart;
 
-        private FillFlowContainer buttons;
+        private readonly FillFlowContainer buttons;
 
         public OsuLogo StartButton;
 

osu.Game/Screens/Select/FooterButton.cs

@@ -51,9 +51,9 @@ namespace osu.Game.Screens.Select
             }
         }
 
-        private SpriteText spriteText;
-        private Box box;
-        private Box light;
+        private readonly SpriteText spriteText;
+        private readonly Box box;
+        private readonly Box light;
 
         public FooterButton()
         {