const-type-layout is a type layout comparison aid, providing a #[derive]able TypeLayout trait that reports:

• The type's name, size, and minimum alignment
• The type's structure, i.e. struct vs. union vs. enum
• Each field's name and offset
• Each variant's name and discriminant

Through the auto-implemented TypeGraphLayout trait, the deep type layout is also reported as a graph.

This crate heavily builds on the original runtime type-layout crate by Lucien Greathouse.

Examples

The layout of types is only defined if they're #[repr(C)]. This crate works on non-#[repr(C)] types, but their layout is unpredictable.

use const_type_layout::TypeLayout;

#[derive(TypeLayout)]
#[repr(C)]
struct Foo {
    a: u8,
    b: u32,
}

assert_eq!(
    format!("{:#?}", Foo::TYPE_LAYOUT),
r#"TypeLayoutInfo {
    name: "mycrate::mymodule::Foo",
    size: 8,
    alignment: 4,
    structure: Struct {
        repr: "C",
        fields: [
            Field {
                name: "a",
                offset: Inhabited(
                    0,
                ),
                ty: "u8",
            },
            Field {
                name: "b",
                offset: Inhabited(
                    4,
                ),
                ty: "u32",
            },
        ],
    },
}"#
);

Over-aligned types have trailing padding, which can be a source of bugs in some FFI scenarios:

use const_type_layout::TypeLayout;

#[derive(TypeLayout)]
#[repr(C, align(128))]
struct OverAligned {
    value: u8,
}

assert_eq!(
    format!("{:#?}", OverAligned::TYPE_LAYOUT),
r#"TypeLayoutInfo {
    name: "mycrate::mymodule::OverAligned",
    size: 128,
    alignment: 128,
    structure: Struct {
        repr: "C,align(128)",
        fields: [
            Field {
                name: "value",
                offset: Inhabited(
                    0,
                ),
                ty: "u8",
            },
        ],
    },
}"#
)

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.