packed structs

[andrewrk]

Packed structs have these properties different than ordinary structs:

• Field order is specified by programmer.
• Field size is specified by programmer.
• Alignment is explicitly specified.

Syntax proposal 1 - attribute:

#attribute("packed")
struct Foo {
    // ...
}

Syntax proposal 2 - keyword:

packed struct Foo {
    // ...
}

It may also be nice to have a way for the programmer to annotate constraints that if violated become compile errors. For example:

• Struct size must be a power of 2, or a multiple of 4.

That's the only example I could think of. And this can be accomplished with

const _ = if (@sizeOf(Foo) % 4 != 0) @compileError("sizeof foo must be multiple of 4") else void;