How Can I Retrieve a Go Function\'s Signature as a String?

Retrieving a Function's Signature as a String in Go

In Go, determining the signature of a function with a specific name and signature within the main package is crucial for providing informative error messages in case of discrepancies.

Can reflect.Type.String() Retrieve the Signature?

While reflect.Type.String() offers the type's name (like main.ModuleInitFunc), it falls short in providing the full signature. This is particularly evident when dealing with function values that have named types.

Constructing the Signature

To construct the signature, we must manually gather information from the reflect.Type.

• Type.In() provides the type of the i^th parameter.
• Type.Out() provides the type of the i^th result type.

Example Implementation

Below is an example function that generates the signature of a function value:

func signature(f interface{}) string {
    t := reflect.TypeOf(f)
    if t.Kind() != reflect.Func {
        return "<not a function>"
    }

    ...

    return buf.String()
}

This function constructs the signature by iterating through the input and output types and assembling them into a human-readable string.

Testing the Signature Function

Testing the signature function yields the following results:

fmt.Println(signature(func(i int) error { return nil })) // func (int) error
fmt.Println(signature(myFunc)) // func (int) error
fmt.Println(signature(time.Now)) // func () time.Time
fmt.Println(signature(os.Open)) // func (string) (*os.File, error)
fmt.Println(signature(log.New)) // func (io.Writer, string, int) *log.Logger
fmt.Println(signature("")) // <not a function>

It's important to note that Go does not provide access to parameter and result type names, so they are omitted from the signature.

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