Why Am I Getting the 'Not Enough Arguments in Call to Method Expression' Error in Go?

How to Avoid the "Not Enough Arguments in Call to Method Expression" Error in Go

While working with Go, you might encounter the following error:

prog.go:18: not enough arguments in call to method expression JSONParser.Parse

This error can be caused by trying to call an instance method as if it were a method at the package scope. In other words, you need to explicitly specify the instance on which you want to call the method.

Consider the following code snippet:

package main

type Schema struct {
}

type JSONParser struct {
}

func (jsonParser JSONParser) Parse(toParse []byte) ([]Schema, int) {
    var schema []Schema
    // whatever parsing logic
    return schema, 0
}

func main() {
    var in []byte
    actual, err2 := JSONParser.Parse(in) // This will result in the error
}

To fix the error, you need to create an instance of the JSONParser type and call the Parse method on that instance. Here's how you can do that:

func main() {
    var in []byte
    jp := JSONParser{} // Create an instance of JSONParser
    actual, err2 := jp.Parse(in) // Call the Parse method on the instance
}

Alternatively, you can define your Parse method as a function without a receiver and call it directly:

func Parse(toParse []byte) ([]Schema, int) {
    var schema []Schema
    // whatever parsing logic
    return schema, 0
}

func main() {
    var in []byte
    actual, err2 := Parse(in) // Call the Parse function directly
}

By explicitly specifying the instance or using a function without a receiver, you can avoid the "not enough arguments in call to method expression" error and call instance methods correctly in Go.

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