CEP-0040: Bodyless Foreign Function Declarations¶

Draft

Draft proposal for bodyless C-style foreign function declarations. V1 imports C functions as explicit function-pointer const values.

Summary¶

Catalyst should eventually decide whether foreign functions can be declared with bodyless fn declarations.

V1 uses @extern(.c) on explicit function-pointer const declarations.

Example¶

Possible future shape:

@extern(.c)
fn puts(text: *const u8) i32

V1 uses an explicit function-pointer constant instead:

@extern(.c)
const puts: *fn (*const u8) callconv(.c) i32

Motivation¶

Bodyless foreign declarations are familiar and concise, but they add a special declaration form and interact with linkage, ABI validation, reflection, and imports.

Proposed Direction¶

The proposal should cover:

source syntax for bodyless foreign functions;
required ABI and link-name metadata;
whether the declaration has function item, function pointer, or special external function type;
reflection and documentation behavior;
diagnostics for unsupported signatures.

V1 Compatibility¶

V1 rejects bodyless C-like function declarations. Use @extern(.c) function-pointer constants.