[Discussion]: Unsigned sizeof

[jnm2]

Proposal document: https://github.com/dotnet/csharplang/pull/9634/files [TEMPORARY URL]

Proposal issue: #9633

[Tinister]

Would/could this also apply for math?

uint totalBytes = ...
uint numElements = totalBytes / sizeof(SomeStruct);

[jnm2]

Yes, the above code would automatically work if sizeof had a conversion to uint.

[colejohnson66]

[333fred]

Most of the time, sizeof is not being used as a constant, because most of the time sizeof is not known at compile time.

[colejohnson66]

At least in my case it is. Things like Win32 interop where you do theThing.cbSize = (uint)sizeof(TheThing). Sure, when you're doing sizeof(T), being explicitly int or uint makes sense, but if T is known at compile time, target-typed makes more sense IMO.

[tannergooding]

You cannot know sizeof(TheThing) at C# compile time, it's dependent on the underlying ABI of the architecture + Operating System.

So the above case is explicitly not being used as a "constant"

[jnm2]

@colejohnson66 It's not constant except for a short predefined list of primitive C# types, like byte. It's nonconstant for everything else, even for concrete types. See https://github.com/dotnet/csharpstandard/blob/draft-v8/standard/expressions.md#12819-the-sizeof-operator. Just imagine a struct with an IntPtr field. That does not have a constant size.

[colejohnson66]

Ah yep. My bad. I forgot that sizeof is implemented at runtime.

https://sharplab.io/#v2:C4LglgNgNAJiDUAfAAgBgATIIwDoBKArgHbBgC2ApjgJIkUBOA9gA4DKDAbmAMYUDOAbgCwAKFHIAzJgBM6ANIQAhnz6iA3qPRbMU4n0UAzCujAl0AFX7AAFAEp0GkdueYA7Oj5gAXhUYHr5gAWFEGmAOa2wk7aAL6icWIiANqswPQE3MAAMooAnowENjn5hXKmMDjsAI4EFCRgitDoAAqK3ADW6AC86Fi2ALriUnxpGcAWwaFEYeqa2pLoBHyBjPTj3ABGrN4UUc4LpuMAao21UTFAA

[h3xds1nz]

Awesome to see a WIP proposal for this, thank you.

[jnm2]

Closing in favor of #5399!

[colejohnson66]

Heh. Of which you commented on the first day it was requested.

[jnm2]

Four years went fast 😅