How do you pass variadic function arguments to other functions in Go?

Understanding Variadic Function Parameter Pass-through

The concept of variadic functions in Go allows functions to accept a variable number of arguments. However, when passing these arguments to other functions, it's crucial to handle the parameter expansion correctly.

Problem:

Consider the following Die function, which serves as a wrapper around fmt.Fprintf:

func Die(format string, args ...interface{}) {
    str := fmt.Sprintf(format, args)
    fmt.Fprintf(os.Stderr, "%v\n", str)
    os.Exit(1)
}

When invoking Die("foo"), the output unexpectedly displays "foo%!(EXTRA []interface {}=[])" instead of just "foo."

Explanation:

Variadic functions treat their arguments as a slice of a particular type. In the Die function, args is a slice of type []interface{}. When passed to fmt.Sprintf, it is treated as a single argument of type []interface{}, not expanding the individual values.

Solution:

To pass individual arguments correctly, use the ... syntax:

str := fmt.Sprintf(format, args...)

This expands the args slice and passes each value as a separate argument.

Additional Information:

The Go specification further clarifies this behavior:

"The type of a variadic function argument is a slice of the type of the individual arguments. Calling a variadic function provides an implicit conversion from a set of provided values to the slice type."

By understanding this concept, you can correctly pass variadic arguments to other functions and avoid unexpected output.

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