Avoid the need for per-settings control classes

osu.Game.Rulesets.Catch/Mods/CatchModDifficultyAdjust.cs

@@ -18,6 +18,8 @@ namespace osu.Game.Rulesets.Catch.Mods
             Precision = 0.1f,
             MinValue = 1,
             MaxValue = 10,
+            ExtendedMaxValue = 11,
+            ReadFromDifficulty = diff => diff.CircleSize,
         };
 
         [SettingSource("Approach Rate", "Override a beatmap's set AR.", LAST_SETTING_ORDER + 1)]
@@ -26,6 +28,8 @@ namespace osu.Game.Rulesets.Catch.Mods
             Precision = 0.1f,
             MinValue = 1,
             MaxValue = 10,
+            ExtendedMaxValue = 11,
+            ReadFromDifficulty = diff => diff.ApproachRate,
         };
 
         [SettingSource("Spicy Patterns", "Adjust the patterns as if Hard Rock is enabled.")]

osu.Game.Rulesets.Osu/Mods/OsuModDifficultyAdjust.cs

@@ -17,15 +17,17 @@ namespace osu.Game.Rulesets.Osu.Mods
             MinValue = 0,
             MaxValue = 10,
             ExtendedMaxValue = 11,
+            ReadFromDifficulty = diff => diff.CircleSize,
         };
 
-        [SettingSource("Approach Rate", "Override a beatmap's set AR.", LAST_SETTING_ORDER + 1, SettingControlType = typeof(ApproachRateSettingsControl))]
+        [SettingSource("Approach Rate", "Override a beatmap's set AR.", LAST_SETTING_ORDER + 1, SettingControlType = typeof(DifficultyAdjustSettingsControl))]
         public DifficultyBindable ApproachRate { get; } = new DifficultyBindable
         {
             Precision = 0.1f,
             MinValue = 0,
             MaxValue = 10,
             ExtendedMaxValue = 11,
+            ReadFromDifficulty = diff => diff.ApproachRate,
         };
 
         public OsuModDifficultyAdjust()

osu.Game.Rulesets.Taiko/Mods/TaikoModDifficultyAdjust.cs

@@ -16,6 +16,7 @@ namespace osu.Game.Rulesets.Taiko.Mods
             Precision = 0.05f,
             MinValue = 0.25f,
             MaxValue = 4,
+            ReadFromDifficulty = _ => 1,
         };
 
         public override string SettingDescription

osu.Game/Rulesets/Mods/ApproachRateSettingsControl.cs

@@ -1,12 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using osu.Game.Beatmaps;
-
-namespace osu.Game.Rulesets.Mods
-{
-    public class ApproachRateSettingsControl : DifficultyAdjustSettingsControl
-    {
-        protected override float UpdateFromDifficulty(BeatmapDifficulty difficulty) => difficulty.ApproachRate;
-    }
-}

osu.Game/Rulesets/Mods/DifficultyAdjustSettingsControl.cs

@@ -11,7 +11,6 @@ using osu.Game.Overlays.Settings;
 
 namespace osu.Game.Rulesets.Mods
 {
-    // TODO: make abstract once we finish making each implementation.
     public class DifficultyAdjustSettingsControl : SettingsItem<float?>
     {
         [Resolved]
@@ -69,14 +68,11 @@ namespace osu.Game.Rulesets.Mods
             if (Current.Value == null)
             {
                 isInternalChange = true;
-                CurrentNumber.Value = UpdateFromDifficulty(difficulty);
+                CurrentNumber.Value = difficultyBindable.ReadFromDifficulty(difficulty);
                 isInternalChange = false;
             }
         }
 
-        // TODO: make abstract
-        protected virtual float UpdateFromDifficulty(BeatmapDifficulty difficulty) => 0;
-
         private class ControlDrawable : CompositeDrawable, IHasCurrentValue<float?>
         {
             private readonly BindableWithCurrent<float?> current = new BindableWithCurrent<float?>();

osu.Game/Rulesets/Mods/DifficultyBindable.cs

@@ -3,6 +3,7 @@
 
 using System;
 using osu.Framework.Bindables;
+using osu.Game.Beatmaps;
 
 namespace osu.Game.Rulesets.Mods
 {
@@ -23,6 +24,11 @@ namespace osu.Game.Rulesets.Mods
             MaxValue = 10,
         };
 
+        /// <summary>
+        /// A function that can extract the current value of this setting from a beatmap difficulty for display purposes.
+        /// </summary>
+        public Func<BeatmapDifficulty, float> ReadFromDifficulty;
+
         public float Precision
         {
             set => CurrentNumber.Precision = value;

osu.Game/Rulesets/Mods/ModDifficultyAdjust.cs

@@ -39,6 +39,7 @@ namespace osu.Game.Rulesets.Mods
             MinValue = 0,
             MaxValue = 10,
             ExtendedMaxValue = 11,
+            ReadFromDifficulty = diff => diff.DrainRate,
         };
 
         [SettingSource("Accuracy", "Override a beatmap's set OD.", LAST_SETTING_ORDER, SettingControlType = typeof(DifficultyAdjustSettingsControl))]
@@ -48,6 +49,7 @@ namespace osu.Game.Rulesets.Mods
             MinValue = 0,
             MaxValue = 10,
             ExtendedMaxValue = 11,
+            ReadFromDifficulty = diff => diff.OverallDifficulty,
         };
 
         [SettingSource("Extended Limits", "Adjust difficulty beyond sane limits.")]