Macro cpp

macro_rules! cpp {
    ({$($body:tt)*}) => { ... };
    ([$($captures:tt)*] $($rest:tt)*) => { ... };
    (unsafe $($tail:tt)*) => { ... };
}

This macro is used to embed arbitrary C++ code.

There are two variants of the cpp! macro. The first variant is used for raw text inclusion. Text is included into the generated C++ file in the order which they were defined, inlining module declarations.

cpp! {{
    #include <stdint.h>
    #include <stdio.h>
}}

The second variant is used to embed C++ code within Rust code. A list of variable names which should be captured are taken as the first argument, with their corresponding C++ type. The body is compiled as a C++ function.

This variant of the macro may only be invoked in expression context, and requires an unsafe block, as it is performing FFI.

let y: i32 = 10;
let mut z: i32 = 20;
let x: i32 = unsafe { cpp!([y as "int32_t", mut z as "int32_t"] -> i32 as "int32_t" {
    z++;
    return y + z;
})};

You can also put the unsafe keyword as the first keyword of the cpp! macro, which has the same effect as putting the whole macro in an unsafe block:

let x: i32 = cpp!(unsafe [y as "int32_t", mut z as "int32_t"] -> i32 as "int32_t" {
    z++;
    return y + z;
});

rust! pseudo-macro

The cpp! macro can contain, in the C++ code, a rust! sub-macro, which allows the inclusion of Rust code in C++ code. This is useful to implement callback or override virtual functions. Example:

trait MyTrait {
   fn compute_value(&self, x : i32) -> i32;
}

cpp!{{
   struct TraitPtr { void *a,*b; };
   class MyClassImpl : public MyClass {
     public:
       TraitPtr m_trait;
       int computeValue(int x) const override {
           return rust!(MCI_computeValue [m_trait : &MyTrait as "TraitPtr", x : i32 as "int"]
               -> i32 as "int" {
               m_trait.compute_value(x)
           });
       }
   }
}}

The syntax for the rust! macro is:

rust!($uniq_ident:ident [$($arg_name:ident : $arg_rust_type:ty as $arg_c_type:tt),*]
     $(-> $ret_rust_type:ty as $rust_c_type:tt)* {$($body:tt)*})

uniq_ident is a unique identifier which will be used to name the extern function