Conversion between Rust String and opaque std_string

I want to call c++ code in my Rust code, so I am using bindgen to generate the FFI code. However, I do not know how to convert the String to string in c++ in my Rust code.

C++ demo code:

#include <string>

class Foo
{
private:
	std::string m_value;

public:
	Foo();
	std::string get_string_value();
	std::string set_string_value(std::string s);
};

Foo::Foo()
{
	m_value = "test";
};

std::string Foo::get_string_value()
{
	return m_value;
}

std::string Foo::set_string_value(std::string s)
{
	m_value = s;
}

build.rs:

	let bindings = bindgen::Builder::default()
		.header("wrapper.hpp")
		.clang_args(&["-x", "c++", "-std=c++11"])
		.allowlist_type("Foo")
		.opaque_type("std::.*")
		.parse_callbacks(Box::new(bindgen::CargoCallbacks))
		.generate()
		.expect("Unable to generate bindings");

The std_string defined in FFI code is like this:

pub type std_string = [u64; 4usize];
#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct Foo {
    pub m_value: std_string,
}
extern "C" {
    #[link_name = "\u{1}_ZN3Foo16get_string_valueB5cxx11Ev"]
    pub fn Foo_get_string_value(this: *mut Foo) -> std_string;
}
extern "C" {
    #[link_name = "\u{1}_ZN3Foo16set_string_valueENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE"]
    pub fn Foo_set_string_value(this: *mut Foo, s: std_string) -> std_string;
}
extern "C" {
    #[link_name = "\u{1}_ZN3FooC1Ev"]
    pub fn Foo_Foo(this: *mut Foo);
}
impl Foo {
    #[inline]
    pub unsafe fn get_string_value(&mut self) -> std_string {
        Foo_get_string_value(self)
    }
    #[inline]
    pub unsafe fn set_string_value(&mut self, s: std_string) -> std_string {
        Foo_set_string_value(self, s)
    }
    #[inline]
    pub unsafe fn new() -> Self {
        let mut __bindgen_tmp = ::std::mem::MaybeUninit::uninit();
        Foo_Foo(__bindgen_tmp.as_mut_ptr());
        __bindgen_tmp.assume_init()
    }
}

How can I use set_string_value() function in my Rust code? It accepts std_string, but I can not convert the String type to std_string type.

Thanks in advance!

Start with build.rs, wrapper.hpp, and the generated std_string and Foo bindings shown in the report. Check bindgen's documented handling of opaque C++ std::string and the ABI of the generated set_string_value signature. Done means establishing a supported way to pass and receive the C++ string, or clearly documenting the required wrapper approach.