idea for a macro that lets you safely mutate some deep field access

mut.nim

import macros

iterator mutIter[T](a: var T): var T =
  yield a

macro mut(a, body: untyped) =
  if a.kind != nnkInfix or a[0].strVal != "as":
    error("Invalid first parameter to `mut`. Usage: `mut <expression> as <name>: <block>`", a)
  let exp = a[1]
  let name = a[2]
  result = quote do:
    for `name` in mutIter(`exp`):
      `body`
  echo repr(result)


when isMainModule:
  type
    Foo = object
      points: array[5, Point]
    Point = object
      x, y: int

  var foo: Foo
  
  mut foo.points[3] as p:
    p.x = 10
    p.y = 20
  
  echo foo