How to Pass Multiple Return Values as Arguments to Another Function in Go?

How to Use Return Values of One Function as Input Arguments to Another

Problem:

Consider two functions, returnIntAndString and doSomething. returnIntAndString returns two values, an integer and a string, while doSomething takes three arguments: a string, an integer, and another string.

When calling doSomething with the return values of returnIntAndString as arguments, the following error occurs:

main.go:45: multiple-value returnIntAndString() in single-value context
main.go:45: not enough arguments in call to doSomething()

Answer:

According to the Go specification, a function call can bind return values of another function to the parameters of the called function only if:

• The number of return values of the first function is equal to the number of parameters for the second function.
• The types of the return values are assignable to the types of the parameters.

In this case, returnIntAndString returns two values, but doSomething requires a third argument. Therefore, this direct invocation is not allowed.

Alternatives:

There are two alternative solutions:

1. Wrap the Return Values in a Struct:

Create a struct that holds the return values of returnIntAndString and pass an instance of that struct to doSomething.

<code class="go">type ReturnValues struct {
    I int
    S string
}

func returnIntAndString() ReturnValues {
    return ReturnValues{42, "Hello"}
}

func doSomething(msg string, values ReturnValues) {
    // Use values.I and values.S as needed
}

doSomething("Message", returnIntAndString())</code>

2. Assign Return Values to Separate Variables:

Assign the return values of returnIntAndString to named variables and pass those variables to doSomething.

<code class="go">var i, s = returnIntAndString()
doSomething("Message", i, s)</code>

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