Nim lacks ref object constructor

[zevv]

Nim lacks a concise ref object constructor. We can do

type Foo = object
  val: int

let f = Foo(val: 13)

but to create a ref Foo I either need to create a separate ref Foo type, or use code like

let f = new Foo
f.val = 13

Leorize suggested the following snippet for this:

proc new[T: ref object | object](o: sink T): auto =                       
  when T is ref:            
    result = o
  else:
    result = new(T)
    result[] = o     

This would allow new to work as a ref object constructor like so:

let f = new Foo(val: 13)

Any feedback on this appreciated, could something like this go in system.nim?

[hlaaftana]

type Foo = object
  val: int

let f = (ref Foo)(val: 13)