[go-nuts] Why is this disallowed by the compiler?

Hi,
Because string and MyType are distinct types, and Go does not perform type
conversions between concrete types.

Thanks,
Josh

--

I understand that. My question is why not.

Am Donnerstag, 13. September 2012 18:19:58 UTC+2 schrieb Josh Holland:

Here's my guess: If they allowed it in function calls they'd probably have
to allow it in method calls, which are really just function calls under the
hood. So given this:

type T1 string
type T2 T1
type T3 T2

func (s T2) f() {}
func (s T3) f() {}

s := "foo"
s.f()


Which f() should be called?

-- L

Because it might be a mistake. Better for the programmer to be explicit.

Russ

--

Type safety.

MyType and string are not the same type, the reason that you can assign "foobar" to a MyType is because it is a literal and I think literals are untyped in go.

--

Hi,

But basically the MyType's memory representation ought to be exactly the
same as string's, right?

The program would never encounter unexpected data hidden beneath a derived
type, it could treat MyType as a string safely.

Am Donnerstag, 13. September 2012 18:29:04 UTC+2 schrieb si guy:

Sort of, but not really. The method sets of "string" and "MyType" would
differ. If you want to pass a MyType to something that expects a string,
convert it. http://golang.org/ref/spec#Conversions There's probably
little or no run-time cost to this, and this makes your intent explicit.

Say you had

type MyType string

func f1(s string) {
s.f2()
}

func (s string) f2() {}
func (s MyType) f2() {}

and you remembered that f1 called f2, and you called f1 with a MyType, you
might easily assume that f1 would call func (s MyType) f2(). But you'd be
wrong.

-- L