How to Perform Type Assertion with Function Type Variables in Go?

Type Assertion with Function Type Variables

This question seeks to understand how to perform type assertion by passing in a type variable into a function. The goal is to achieve something like the following:

// Pseudocode
func myfunction(mystring string, mytype Type) {
    ...

    someInterface := translate(mystring)
    object, ok := someInterface.(mytype)

    ...  // Do other stuff
}

func main() {
    // Desired function call
    myfunction("hello world", map[string]string)
}

Proper Function Declaration for Type Assertion

In order to perform the type assertion in the given function, the proper function declaration should use interface{} for the type parameter. This is because interfaces in Go can hold any type value. Here's a corrected version of the function declaration:

func myfunction(v interface{}, expectedType interface{}) bool {
    return reflect.TypeOf(v) == reflect.TypeOf(expectedType)
}

Usage in the Main Function

In the main function, the myfunction can be called by passing in a sample value of the desired type instead of the type itself:

assertNoMatch := myfunction("hello world", map[string]string{})

assertMatch := myfunction("hello world", "stringSample")

fmt.Printf("%+v\n", assertNoMatch)  // false
fmt.Printf("%+v\n", assertMatch)  // true

Approach Explained

The approach uses the reflect package to compare the type of the actual value (v) with a sample value of the expected type (expectedType). This allows us to perform dynamic type checks, just as if we were using a switch statement to check the type of mystring and casting it to the desired type explicitly.

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