Expand description
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.