`ref` type and `mut` type

[ryo33]

'ref type is something like a Arc<T> and 'mut type is something like a Arc<Mutex<T>>.

Syntax

<'ref 'nat> 'ref 1

$ <'mut 'nat> 'mut 1;
// update the value
'mutate & 'mut 'nat & \ 'nat -> 'nat