Functions

Any function can be exported as long as its argument types and return type are compatible with Julia. This requires that these types implement CCallArg and CCallReturn respectively.

These traits should not be implemented manually. jlrs provides implementations for primitive and managed types, bindings for Julia types generated with JlrsCore.Reflect.reflect will derive these traits when applicable. CCallArg is derived if the type has no elided type parameters¹, isn't a zero-sized type, and is immutable. CCallReturn additionally requires that the type is an isbits type. If these properties hold, the data can be taken or returned by value, and the layout of the Rust type maps to a single Julia type.

Exporting a function is a matter copying and pasting its signature:

use jlrs::prelude::*;

fn add(a: f64, b: f64) -> f64 {
    a + b
}

julia_module! {
    become julia_module_tutorial_init_fn;

    fn add(a: f64, b: f64) -> f64;
}

julia> module JuliaModuleTutorial ... end
Main.JuliaModuleTutorial

julia> JuliaModuleTutorial.add(1.0, 2.0)
3.0

julia> JuliaModuleTutorial.add(1, 2.0)
ERROR: MethodError: no method matching add(::Int64, ::Float64)

We don't have to mark our function as extern "C", the julia_module! macro generates an extern "C" wrapper function for every exported function. These wrappers only exist inside the julia_module_tutorial_init_fn so we don't need to worry about name conflicts.

Like constants, exported functions can be renamed and documented.

use jlrs::prelude::*;

fn add(a: f64, b: f64) -> f64 {
    a + b
}

julia_module! {
    become julia_module_tutorial_init_fn;

    ///     add!(::Float64, ::Float64)::Float64
    fn add(a: f64, b: f64) -> f64 as add!;
}

julia> module JuliaModuleTutorial ... end
Main.JuliaModuleTutorial

julia> JuliaModuleTutorial.add!(1.0, 2.0)
3.0

help?> JuliaModuleTutorial.add!
   add!(::Float64, ::Float64)::Float64