When and Why Use Unnamed Function Arguments in Go?

Unnamed Function Arguments in Go

Go allows function arguments to be left unnamed, which may initially seem confusing. However, this feature serves several purposes and has clear syntax rules.

According to the Go specification, ParameterDecl (parameter declaration) is:

ParameterDecl  = [ IdentifierList ] [ "..." ] Type .

The IdentifierList (the identifier name or names) is optional, indicating that only the Type is required.

Why use unnamed arguments?

Unnamed arguments are typically used in scenarios where:

• The parameter is present but not used/referenced. This occurs when a function wants to implement an interface or pass a function value with a specific signature.
• Documentation. Unnamed parameters convey that the argument is not intended to be used.
• Forward compatibility. When updating a library, additional parameters can be introduced without breaking backward compatibility by leaving them unnamed.

Syntax rules

Mixing named and unnamed parameters is not allowed. If some parameters are named, all must be named. Alternatively, the blank identifier (_) can be used to indicate that a parameter should not be referenced.

Example

Consider the MyWriter interface:

type MyWriter interface {
    Write(p []byte) error
}

An implementation of this interface that discards data could be written as follows:

type DiscardWriter struct{}

func (DiscardWriter) Write([]byte) error { return nil }

The DiscardWriter type has an unnamed parameter because it does not use the argument passed to the Write method.

In conclusion, unnamed function arguments in Go provide flexibility and clarity when dealing with parameters that are present but not used. They facilitate interface implementation, document unused parameters, and allow for future expansion without breaking backward compatibility.

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