.NET 3.5 via MonoMod.Backports #540
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Backports has a few of these shims already, on |
Yes, I intend to only include MonoMod.Backports when absolutely necessary (i.e., only for the .NET 3.5 target). Using the existing shims for |
| /// <summary> | ||
| /// Gets a value indicating whether the current runtime runs on the Microsoft Windows operating system. | ||
| /// </summary> | ||
| public static bool IsRunningOnWindows | ||
| { | ||
| get; | ||
| } | ||
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| /// <summary> | ||
| /// Gets a value indicating whether the current runtime runs on a Unix-based operating system. | ||
| /// </summary> | ||
| public static bool IsRunningOnUnix | ||
| { | ||
| get; | ||
| } |
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I think it's more efficient to not cache the value because then the JIT can optimize branching based on runtime information.
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As long as the static constructor has run when the JIT compiles a method using it, it will see this as a constant (because it gets emitted as a static readonly field, through a very small method body).
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I'm pretty sure it will also depend on whether the calls to into RuntimeInformation are considered JIT intrinsics, which I am not sure about.
| /// <summary> | ||
| /// Obtains a singleton instance of an empty array of the provided type. | ||
| /// </summary> | ||
| /// <typeparam name="T">The type to get the empty array for.</typeparam> | ||
| /// <returns>The empty array.</returns> | ||
| #if !NET35 | ||
| public static T[] Empty<T>() => Array.Empty<T>(); | ||
| #else | ||
| public static T[] Empty<T>() => ArrayHelper<T>.Empty; | ||
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| private static class ArrayHelper<T> | ||
| { | ||
| public static readonly T[] Empty = new T[0]; | ||
| } | ||
| #endif |
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Collection expressions might be supported on NET35. If so, I think you could use [] everywhere instead of having a shim.
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I think that when Array.Empty<T>() is not available, [] will always construct a new array. Probably worth double checking though.
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This is indeed the case. On .NET 3.5 the following C#
public static int[] ReturnEmpty() => [];results in the following CIL, creating a new empty array on every call.
.method public static hidebysig int32[] ReturnEmpty() cil managed
{
.maxstack 8
IL_0000: ldc.i4.0
IL_0001: newarr valuetype [mscorlib] System.Int32
IL_0006: ret
}
MemoryMappedFile for .NET Framework 3.5
IInputFile::BaseAddressMemoryMappedDataSource, the new implementation usesUnmanagedDataSource.Closes #536