{
//...
        "code":
        {
            "code": "E0764",
            "explanation": "A mutable reference was used in a constant.\n\nErroneous code example:\n\n```compile_fail,E0764\nfn main() {\n    const OH_NO: &'static mut usize = &mut 1; // error!\n}\n```\n\nMutable references (`&mut`) can only be used in constant functions, not statics\nor constants. This limitation exists to prevent the creation of constants that\nhave a mutable reference in their final value. If you had a constant of\n`&mut i32` type, you could modify the value through that reference, making the\nconstant essentially mutable.\n\nWhile there could be a more fine-grained scheme in the future that allows\nmutable references if they are not \"leaked\" to the final value, a more\nconservative approach was chosen for now. `const fn` do not have this problem,\nas the borrow checker will prevent the `const fn` from returning new mutable\nreferences.\n\nRemember: you cannot use a function call inside a constant or static. However,\nyou can totally use it in constant functions:\n\n```\nconst fn foo(x: usize) -> usize {\n    let mut y = 1;\n    let z = &mut y;\n    *z += x;\n    y\n}\n\nfn main() {\n    const FOO: usize = foo(10); // ok!\n}\n```\n"
        },
// ...
}

{
// ...
       "code":
        {
            "code": "E0764"
        }
// ...
}