nimforum mirror - Passing X to a sink parameter introduces an implicit copy

...; if possible, rearrange your program's control flow to prevent it.

This is a common hint message I've been getting.

Are there any guidelines as to how to deal with that? (I know about move, but I'm not really sure what it implies...)

Was wondering the same thing

a couple simple illustrations:

proc sinkingLen(x: sink seq[int]):int = x.len
var s = @[1,2,3,4]
echo s.sinkingLen

this warns, because s is a global variable. you can either explicitly move s:

echo sinkingLen(move(s))
echo s #s becomes @[] after the move

or wrap everything in a main proc

proc main()=
  var s = @[1,2,3,4]
  echo s.sinkingLen
  echo s

but wait, here s is used after sinking into sinkingLen, so the compiler still warns. you can solve this by rearranging:

proc main()=
  var s = @[1,2,3,4]
  echo s
  echo s.sinkingLen

Nice explanation. Thanks!

I'll give it a try to see the results...

For code that is not performance critical you can also simply disable the warning.

Mirror of forum.nim-lang.org