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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.

```rust use consttypelayout::TypeLayout;

[derive(TypeLayout)]

[repr(C)]

struct Foo { a: u8, b: u32, }

println!("{:#?}", Foo::TYPE_LAYOUT); // prints: // // TypeLayoutInfo { // name: "Foo", // size: 8, // alignment: 4, // structure: Struct { // repr: "C", // fields: [ // Field { // name: "a", // offset: 0, // ty: "u8", // }, // Field { // name: "b", // offset: 4, // ty: "u32", // }, // ], // }, // } ```

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

```rust use consttypelayout::TypeLayout;

[derive(TypeLayout)]

[repr(C, align(128))]

struct OverAligned { value: u8, }

println!("{:#?}", OverAligned::TYPE_LAYOUT); // prints: // // TypeLayoutInfo { // name: "OverAligned", // size: 128, // alignment: 128, // structure: Struct { // repr: "C,align(128)", // fields: [ // Field { // name: "value", // offset: 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.