#[derive(StructGetMutField)] to get field without specifying the field name

[nielsle]

Here is another idea that might be useful. It could be nice to have a generic macro to get a field without specifying the field name

struct A;
struct B;

#[derive(StructGetMutField)]
struct Foo {
    a:A,
    b:B,
}

fn main() {
    let foo= Foo {a:A, b:B};
    let _a: &A = foo.get_mut_field();
    let _b: &B = foo.get_mut_field();
}

The following could be derived behind the scenes

trait GetMutField<T>   {
    fn get_mut_field(&mut self) ->&mut T;
}

impl GetMutField<A> for Foo {
    fn get_mut_field(&mut self) ->&mut A {&mut self.a}
}

impl GetMutField<B> for Foo {
    fn get_mut_field(&mut self) ->&mut B {&mut self.b}
}

This macro would allow me to do the following with minimal boiler plate code;

#[derive(StructGetMutField)]
struct Foo {
    as:Vec<A>,
    bs:Vec<B>,
}

let mut foo = Foo {as:Vec::new(), bs:Vec::new(), };
let a = A;
foo.get_mut_field().push(a);

Similarly it would allow me to create a poor mans TypeMap without using the Any-trait.

#[derive(StructGetMutField)]
struct Foo {
    a_opt:Option<A>,
    b_opt:Option<B>,
}

let mut foo = Foo {a_opt: Option::new(), b_opt: Option::new(), };
foo.get_mut_field() = Some(A);;