fn set_elem(vm: &mut VM, self_val: Value, args: &Args2) -> VMResult {
    args.check_args_range(2, 3)?;
    self_val.into_array().set_elem(vm.args())
}
## instance method Array#[]=
- self[[nth]] = val
- self[[range]] = val
- self[[start, length]] = val

https://docs.ruby-lang.org/ja/latest/method/Array/i/=5b=5d=3d.html
ruruby/src/builtin/array.rs