assign a string type golang

Question

I'm having a hard time assigned a string to a type string. So I have this type:

type Username string

I then have a function that returns a string

What I'm trying to do is set username to that returned string:

u := &Username{returnedString}

I also tried

var u Username
u = returnedString

But I always get an error.

Answer 1

As others have pointed out, you'll need to do an explicit type conversion:

someString := funcThatReturnsString()
u := Username(someString)

I'd recommend reading this article on implicit type conversion. Specifically, Honnef references Go's specifications on assignability:

A value x is assignable to a variable of type T ("x is assignable to T") in any of these cases:

• x's type V and T have identical underlying types and at least one of V or T is not a named type.

So in your example, the returnedString is already a "named type": it has type string. If you had instead done something like

var u Username
u = "some string"

you would have been ok, as the "some string" would be implicitly converted into type Username and both string and Username have the underlying type of string.