Champion "Native-Sized Number Types" (VS 16.8, .NET 5)

[gafter]

Summary: nint i = 1; and nuint i2 = 2;

Shipped in preview in 16.7p1.

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• Proposal added (https://github.com/dotnet/csharplang/blob/master/proposals/csharp-9.0/native-integers.md, open issues Open LDM issues with native integers #3259)
• Discussed in LDM
• Decision in LDM
• Finalized (done, rejected, inactive)
• Spec'ed

/cc @KrzysztofCwalina @jaredpar

[jcouv update:] as part of this feature, we should consider what Interlocked overloads the BCL/runtime should provide for those new types.

[jkotas]

Proposal: dotnet/corefxlab#1471

[CyrusNajmabadi]

nuint... :)

[jnm2]

Actually, could C# add nint, nunit, and nfloat?

[CyrusNajmabadi]

As i mentioned in the other proposal, i don't see a lot of value in C# adding any keywords here. IntN, FloatN and the like are totally reasonable names to just use as is. And if you really want a all-lower name, then just add using nint = System.IntN.

[jnm2]

Do you foresee people opting to use IntN over int as iteration variables?

[CyrusNajmabadi]

@jnm2 i'm not sure what you mean? Can you give an example? I don't generally think about iteration as being related to native sized ints... so i'm not sure what the connection is. Thanks!

[jnm2]

@CyrusNajmabadi Just a plain for loop for example. Everyone defaults to int for the iteration variable type, but would IntN potentially eke out more performance than int on x64?

[CyrusNajmabadi]

I would really hope not :) But i'll let the CLR guys weigh in on that.

[jkotas]

would IntN potentially eke out more performance than int on x64?

native int is more performant than int32 for loops that iterate over memory on 64-bit platforms. int32 tend to require int32->native int casts that are unnecessary overhead. E.g. Check how some methods on Span<T> have been optimized to avoid the extra overhead: https://github.com/dotnet/corefx/blob/master/src/System.Memory/src/System/SpanHelpers.byte.cs#L76

[jveselka]

I wonder, should nint/nuint be allowed as underlying type of enums as well? And nint/nuint consts?

[bbarry]

@zippec that would be a breaking change in struct layouts wouldn't it?

[tannergooding]

@bbarry, how would that be a breaking change? Only new enums would support being subclassed from nint/nuint and the runtime already supports said functionality.

The runtime also supports native sized constants (although they are actually 32-bit constants that are implicitly converted)