Crate type_layout

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

• The type's name, size, and minimum alignment
• Each field's name, type, offset, and size
• Padding due to alignment requirements

type-layout currently only functions on structs with named fields. This is a temporary limitation.

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 type_layout::TypeLayout;

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

println!("{}", Foo::type_layout());
// prints:
// Foo (size 8, alignment 4)
// | Offset | Name      | Size |
// | ------ | --------- | ---- |
// | 0      | a         | 1    |
// | 1      | [padding] | 3    |
// | 4      | b         | 4    |

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

use type_layout::TypeLayout;

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

println!("{}", OverAligned::type_layout());
// prints:
// OverAligned (size 128, alignment 128)
// | Offset | Name      | Size |
// | ------ | --------- | ---- |
// | 0      | value     | 1    |
// | 1      | [padding] | 127  |

Minimum Supported Rust Version (MSRV)

type-layout supports Rust 1.34.1 and newer. Until type-layout reaches 1.0, changes to the MSRV will require major version bumps. After 1.0, MSRV changes will only require minor version bumps, but will need significant justification.

Structs

TypeLayoutInfo

Enums

Field

Traits

TypeLayout

Derive Macros

TypeLayout