Re: Iterator invalidation

[StasB]

Here's a simple proof of concept: 
    
    
    import macros
    
    type Mut = object
    
    proc messUpMySeq(s: var seq[int]) {.tags: [Mut].} =
      s.add(123)
    
    iterator foo[T](s: seq[T]): T =
      var i = 0
      while i < s.len:
        yield s[i]
        inc i
    
    macro safeFor(binding, it, body): untyped =
      quote do:
        (proc() {.tags: [].}  =
          for `binding` in `it`:
            `body`)()
    
    var s = @[1, 2, 3, 4, 5]
    
    safeFor t, foo(s):
      messUpMySeq(s)
      echo t
    

Unfortunately, this requires a custom `for`.