Taking single value from multi-return function and inlining function calls

[Tanmay Das]

Hi,

I am relatively new to the Go language, and I have always wanted to ask this question:

Consider the following snippet:

package main

import "fmt"

func returnMany() (int, int) {
    return 4, 2
}

func useOne(value int) {
    fmt.Println(value)
}

func main() {
    useOne(returnMany())
}

The returnMany function returns multiple values and the useOne function accepts only a single value. I have often come across situations where the returnMany() resides in my codebase and the useOne() comes from an external library.

The code above obviously fails to build. Typically as a consumer of "useOne" package, I know which value it expects and I can either do this:

value, _ := returnMany()
useOne(value)

Or, this, depending on my need:

_, value := returnMany()
useOne(value)

This makes inlining function calls impossible and adds a little bit of noise to the codebase, IMO.

Is there a way I can inline this without introducing a temp variable? Pseudocode example:

useOne(returnMany()[1]) // 4
useOne(returnMany()[2]) // 2

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

[Axel Wagner]

You could write helpers:

func Left[A, B any](a A, b B) A { return a }

func Right[A, B any](a A, b B) B { return b }

Which you can then insert

useOne(Left(returnMany())

useOne(Right(returnMany())

But TBQH, I would not consider this good style. It ultimately adds more noise and overhead, as people now have to figure out what Left and Right do (you might argue that they should be named better, but still).

The right thing to do here, in my opinion, is to just accept the extra statement. Yes, it's a little bit more noisy. But it's not a dramatic enough different to justify deviating from what the core language gives you.

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[Aaron Rubesh]

Another option for this is if your function is always called after the call to the external library, you can change your function signature to match the return value of the external library. 

Its quite common to see something like this:

`

func A() (int, error) {} 

func UseA(a int, err error) (int, error) {

  if err != nil {return err} 

  ....

}

... 

UseA(A()) 

`

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---

From: 'Axel Wagner' via golang-nuts <golan...@googlegroups.com>
Sent: Monday, August 29, 2022 3:58:38 AM
To: Tanmay Das <tanma...@gmail.com>
Cc: golang-nuts <golan...@googlegroups.com>
Subject: Re: [go-nuts] Taking single value from multi-return function and inlining function calls

 

To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAEkBMfEvVVrHjBH8RZ7QBrHjsiqXFzqSveKsZhd7of6ZxoWCjw%40mail.gmail.com.