How to handle size of items defined in third party crates?

[little-dude]

Hi,

This crate relies on SizeOf being implemented for the types we're interested in. There are two issues with this:

• users of size-of can't implement this trait directly for types that are defined in dependencies. The only solution that comes to mind is to create wrappers for these types and implement size-of for these wrappers.
• even then, implementing SizeOf requires looking at the target type layout. The problem is that many crates don't expose the internals of the types they expose, and because these details are not part of the public API, they can change with any version bump, making our SizeOf impls inaccurate.

Do you have plans/ideas/recommendations to mitigate these issues?

[little-dude]

One case I often have is this:

struct Foo {
    a: String,
    b: u32
    // potentially other fields which implement SizeOf
    // ...
    // ...
    // And finally a single field which uses a type that doesn't implement `SizeOf`
    oops: some_crate::SomeType
}

It's annoying to have to write the SizeOf impl manually just because of one field. Maybe an attribute like:

#[derive(SizeOf)]
struct Foo {
    a: String,
    b: u32
    #[size_of(with = "size_of_some_type")]
    oops: some_crate::SomeType
}

fn size_of_some_type(value: &some_crate::SomeType, &mut Context {
    // impl goes here
}

[Kixiron]

There's a #[size_of(skip)] attribute, I'm working on a with attribute as well