[golang check if struct is a specific type] #go #golang #struct #type #assert #check

golang check if struct is a specific type.go

package main

import "fmt"

type Test struct {
	foo int
}

type TestA struct {
	Test
}

type TestB struct {
	Test
}

func isTest(t interface{}) string {
	switch t.(type) {
	case TestA:
		return "A"
	case TestB:
		return "B"
	default:
		return "NA"
	}
}

func main() {
	ta := TestA{}
	tb := TestB{}

	// by not setting 'foo' property as part of TestA/TestB instantiation
    // we avoid the "cannot use promoted field" compiler error
    // see: https://gist.github.com/Integralist/b123e4a98bcf232d09216577c29f34a3
	ta.foo = 1
	tb.foo = 2
  
    /*
     a better approach to avoid the "cannot use promoted field" compiler error
     would be to do this...
     
     t := Test{foo: 123}
     ta := TestA{t}
     tb := TestB{t}
    */

	fmt.Printf("%+v\n", ta)
	fmt.Printf("%+v\n", tb)

	fmt.Println(isTest(ta)) // A
	fmt.Println(isTest(tb)) // B
}