Comment by Groxx

https://github.com/sourcegraph/conc/blob/main/iter/iter.go#L...

    // Map applies f to each element of input, returning the mapped result.
    func Map[T, R any](input []T, f func(*T) R) []R {
     res := make([]R, len(input))
     ForEachIdx(input, func(i int, t *T) {
      res[i] = f(t)
     })
     return res
    }

Seems a little silly to farm that off to a custom func when you could just write the for-loop, but it's probably fine / may be no different in practice.

Let's go see what ForEach does, to make sure: https://github.com/sourcegraph/conc/blob/main/iter/iter.go#L...

    // ForEachIdx is the same as ForEach except it also provides the
    // index of the element to the callback.
    func ForEachIdx[T any](input []T, f func(int, *T)) {
     numTasks := runtime.GOMAXPROCS(0)
     numInput := len(input)
     if numTasks > numInput {
      // No more tasks than the number of input items.
      numTasks = numInput
     }
    
     var idx atomic.Int64
     // Create the task outside the loop to avoid extra closure allocations.
     task := func() {
      i := int(idx.Add(1) - 1)
      for ; i < numInput; i = int(idx.Add(1) - 1) {
       f(i, &input[i])
      }
     }
    
     var wg conc.WaitGroup
     for i := 0; i < numTasks; i++ {
      wg.Go(task)
     }
     wg.Wait()
    }

Yeah I'm gonna go with a giant nope. Getting that through review is rather concerning to say the least, for something you'd be basing your most-complex and most-needing-correctness code around.