I have a question. I know the below code snippet will return error due to _inva . . .

Programming Golang
#1

Ximeng Zhao:
I have a question. I know the below code snippet will return error due to invalid operation: str + nativeStr (mismatched types MyString and string)

type MyString string

func main() {
	str := MyString("Hello")
	nativeStr := " World!"
	result := str + nativeStr // error happens here
	fmt.Println(result)
}

But why it doesn’t throw error when I do str + " World!" in the fmt.Println()

type MyString string

func main() {
	str := MyString("Hello")
	fmt.Println(str + " World!")
}

My thought was to add string() around str such as

fmt.Println(string(str) + " World!")

Thank you!

#2

Alistair Mackay:
The compiler is very fussy about trying to mix types without an explicit cast (as in your 3rd code block). They enforce this for clarity of the code.

So

result := str + nativeStr // error happens here

It will refuse to implicitly cast string to MyString

result := str + " World!" // no error

It will implicitly cast a string literal to MyString because it knows that MyString is really just a string.

result := string(str) + " World!"

Unnecessary explicit cast

Same goes for numeric types like int and float64. If you add values of these types in any other language, you get a float64 result. Go will refuse the addition unless both values are exactly the same type, i.e. you must cast one of the operands.

	var i int = 1
	var f float64 = 2.0
	
	_ = i + f  // compiler error - no cast
	_ = i + 1  // ok to add numeric literal
	_ = f + 1  // ok to add numeric literal
#3

Ximeng Zhao:
Thanks @Alistair Mackay, that’s super helpful to know :slightly_smiling_face: