Bug 19605 – invalid forward reference error when getting the `.sizeof` of an opaque enum

Very easy to reproduce: ``` enum X; static assert(X.sizeof == 0); ``` Note that I'm not exactly sure what the size of this should be. My guess was 0, but DMD 2.064 seems to manage to evaluate it to 4 despite still issuing the same error.

(In reply to elpenguino+D from comment #0) > Very easy to reproduce: > ``` > enum X; > static assert(X.sizeof == 0); > ``` > > Note that I'm not exactly sure what the size of this should be. My guess was > 0, but DMD 2.064 seems to manage to evaluate it to 4 despite still issuing > the same It is 4 because it is the same as sizeof int. I will look into the error. [1] https://dlang.org/spec/enum.html

@Basile-z created dlang/dmd pull request #9460 "fix issue 19605 - invalid forward reference error when getting the `sizeof` of an opaque enum" fixing this issue: - fix issue 19605 - invalid forward reference error when getting the `.sizeof` of an opaque enum https://github.com/dlang/dmd/pull/9460

This one might be invalid actually. The implementation of the fix is problematic at least.

sizeof is defined as being the size in bytes of an expression. It does not mean "the amount of bytes required for a variable to be stored in memory at program runtime". In this case, the compiler correctly reports that it uses 4 bytes to store the enumeration, even though it is empty. I guess this could be improved, however, that would make the code uglier. This way the compiler code treats empty enums and non-empty enums the same. The cost is that you may use some extra bytes at compile time. My take on this is that this is an invalid bug report, however, I am open to other perspectives.

The spurious error is gone anyway.