Why does "foo%!(EXTRA []interface {}=[])" appear when calling a `fmt.Fprintf` wrapper with variadic arguments?

Variadic Function Argument Pass-Through Issue in fmt.Fprintf Wrapper

This article addresses an issue encountered when creating a simple fmt.Fprintf wrapper that accepts a variable number of arguments.

Problem: Incorrect Output When Calling Wrapper

When calling the wrapper function Die("foo"), an unexpected output is produced: "foo%!(EXTRA []interface {}=[])". This raises two questions:

• Why does this extra text appear after "foo"?
• What is the correct way to create wrappers around fmt.Fprintf?

Solution: Using Spread Operator

Variadic functions in Go receive arguments as a slice. In this case, the wrapper function Die has a parameter args of type []interface{}. However, when passing this argument to fmt.Sprintf, it is treated as a single argument of type []interface{}.

To resolve this issue and pass each value in args as a separate argument, the spread operator (...) must be used. By adding this syntax to the fmt.Sprintf call, the individual values in args are expanded and passed accordingly:

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

This approach ensures that the wrapper function correctly passes the variable arguments to fmt.Fprintf.

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