There is no tuple type in go. When you see a func() (A, error) that is not a function returning a tuple. It is a function returning two values that cannot be composed. You can't A(B()) if B returns two values. It's pure comedy.

> You can't A(B()) if B returns two values.

You can if A is a function which takes two arguments, e.g.

  package main

  import "log"

  func A(x, y int) { log.Printf("%d, %d", x, y) }
  func B() (int, int) { return 1, 2 }
  func main() { A(B()) }

https://go.dev/play/p/Jp4B0L6NJj2

What you can't do is a(b(), c()) unless b and c return single values.

And there are no slices or channels of tuples, return values must be destructured right away.