Increase priority of MemoryMarshal.AsRef<T>(Span<T>) with [OverloadResolutionPriority] #122217
Description
Description
There is:
ref T AsRef<T>(Span<byte> span)
ref readonly T AsRef<T>(ReadOnlySpan<byte> span)in System.Runtime.InteropServices.MemoryMarshal and I propose adding [OverloadResolutionPriority(1)] attribute to the AsRef<T>(Span<byte>) overload as follows:
[OverloadResolutionPriority(1)]
ref T AsRef<T>(Span<byte> span)
ref readonly T AsRef<T>(ReadOnlySpan<byte> span)That would solve the issue described below.
Unfortunately, the usage of the first overload is impaired by changes from C# 14. I've described the issue here: dotnet/roslyn#81528 (comment) and have been told the change is intended.
Assuming we have:
public struct MyStruct
{
public static implicit operator Span<byte>(in MyStruct value) => default;
}Then, with C# 13 the following worked:
void M()
{
// Overload AsRef<byte>(Span<byte>) is selected.
ref var r = ref MemoryMarshal.AsRef<byte>(x);
}but with C# 14 following happens:
void M()
{
// Does not compile. Overload AsRef<byte>(ReadOnlySpan<byte>) is selected, so `ref var` cannot be used.
ref var r = ref MemoryMarshal.AsRef<byte>(x);
// Compiles, but that's not what I want (I want 'ref var' and not 'ref readonly var').
ref readonly var r2 = ref MemoryMarshal.AsRef<byte>(x);
}The workaround is to use the explicit cast:
void M()
{
// Compiles, but an explicit cast is needed to select the correct overload.
ref var r = ref MemoryMarshal.AsRef<byte>((Span<byte>)x);
}Reproduction Steps
public struct MyStruct
{
public static implicit operator Span<byte>(in MyStruct value) => default;
}
void M()
{
ref var r = ref MemoryMarshal.AsRef<byte>(x);
}Expected behavior
The following should compile with C# 14 (as it compiled with C# 13).
public struct MyStruct
{
public static implicit operator Span<byte>(in MyStruct value) => default;
}
void M()
{
ref var r = ref MemoryMarshal.AsRef<byte>(x);
}Actual behavior
The following does not compile with C# 14.
public struct MyStruct
{
public static implicit operator Span<byte>(in MyStruct value) => default;
}
void M()
{
ref var r = ref MemoryMarshal.AsRef<byte>(x);
}Regression?
It worked with C# 13.
Known Workarounds
Use explicit cast (instead of implicit) to Span<byte>.
Configuration
No response
Other information
No response