Return values of function as input arguments to another - go

Question

If I have
func returnIntAndString() (i int, s string) {...}
And I have:
func doSomething(i int, s string) {...}
Then I can do the following successfully:
doSomething(returnIntAndString())
However, let's say I want to add another argument to doSomething like:
func doSomething(msg string, i int, s string) {...}
Go complains when compiling if I call it like:
doSomething("message", returnIntAndString())
With:
main.go:45: multiple-value returnIntAndString() in single-value context
main.go:45: not enough arguments in call to doSomething()
Is there a way to do this or should I just give up and assign the return values from returnIntAndString to some references and pass msg and these values like doSomething(msg, code, str) ?

Answer 1

It's described here in the spec. It requires the inner function to return the correct types for all arguments. There is no allowance for extra parameters along with a function that returns multiple values.
As a special case, if the return values of a function or method g are
equal in number and individually assignable to the parameters of
another function or method f, then the call f(g(parameters_of_g)) will
invoke f after binding the return values of g to the parameters of f
in order. The call of f must contain no parameters other than the call
of g, and g must have at least one return value. If f has a final ...
parameter, it is assigned the return values of g that remain after
assignment of regular parameters.
func Split(s string, pos int) (string, string) {
return s[0:pos], s[pos:]
}
func Join(s, t string) string {
return s + t
}
if Join(Split(value, len(value)/2)) != value {
log.Panic("test fails")
}
If those specific conditions are not met, then you need to assign the return values and call the function separately.

Answer 2

I had the same question. The best solution I could come up with is creating types or structs for my desired extra parameters and writing methods for them like this:
package main
import (
"fmt"
)
type Message string
type MessageNumber struct {
Message string
Number int
}
func testfunc() (foo int, bar int) {
foo = 4
bar = 2
return
}
func (baz Message) testfunc2(foo int, bar int) {
fmt.Println(foo, bar, baz)
}
func (baz MessageNumber) testfunc3(foo int, bar int) {
fmt.Println(foo, bar, baz.Number, baz.Message)
}
func main() {
Message("the answer").testfunc2(testfunc())
MessageNumber{"what were we talking about again?", 0}.testfunc3(testfunc())
fmt.Println("Done. Have a day.")
}
The output looks like this:
user#Frodos-Atari-MEGA-STE:~/go/test$ go run main.go
4 2 the answer
4 2 0 what were we talking about again?
Done. Have a day.