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Add enums to Enumerable.Order implicitly stable check #99533

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Merged
merged 3 commits into from
Mar 12, 2024
Merged

Add enums to Enumerable.Order implicitly stable check #99533

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c7bc23b
Add enums to Enumerable.Order implicitly stable check
stephentoub Mar 11, 2024
a713481
Merge branch 'main' into enumorder
stephentoub Mar 11, 2024
f069619
Address PR feedback
stephentoub Mar 11, 2024
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29 changes: 21 additions & 8 deletions src/libraries/System.Linq/src/System/Linq/OrderBy.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -140,14 +140,27 @@ public static IOrderedEnumerable<TSource> ThenByDescending<TSource, TKey>(this I

/// <summary>Gets whether the results of an unstable sort will be observably the same as a stable sort.</summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static bool TypeIsImplicitlyStable<T>() =>
typeof(T) == typeof(sbyte) || typeof(T) == typeof(byte) ||
typeof(T) == typeof(int) || typeof(T) == typeof(uint) ||
typeof(T) == typeof(short) || typeof(T) == typeof(ushort) ||
typeof(T) == typeof(long) || typeof(T) == typeof(ulong) ||
typeof(T) == typeof(Int128) || typeof(T) == typeof(UInt128) ||
typeof(T) == typeof(nint) || typeof(T) == typeof(nuint) ||
typeof(T) == typeof(bool) || typeof(T) == typeof(char);
internal static bool TypeIsImplicitlyStable<T>()
{
Type t = typeof(T);
if (typeof(T).IsEnum)
{
t = typeof(T).GetEnumUnderlyingType();
}

// Check for integral primitive types that compare equally iff they have the same bit pattern.
// bool is included because, even though technically it can have 256 different values, anything
// other than 0/1 is only producible using unsafe code. It's tempting to include a type like string
// here, as it's so commonly used with ordering, but two different string objects can compare equally,
// and their reference identity can be observable in a stable vs unstable sort.
return
t == typeof(sbyte) || t == typeof(byte) || t == typeof(bool) ||
t == typeof(short) || t == typeof(ushort) || t == typeof(char) ||
t == typeof(int) || t == typeof(uint) ||
t == typeof(long) || t == typeof(ulong) ||
t == typeof(Int128) || t == typeof(UInt128) ||
t == typeof(nint) || t == typeof(nuint);
}
}

public interface IOrderedEnumerable<out TElement> : IEnumerable<TElement>
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