On Thu, 10 May 2018 08:33:32 +0000
Jan Mercl <[email protected]> wrote:
> This modified example from another thread does not compile:
You modified it in a pretty significant way. The original example had
type T = *T
which is a recursive type alias (which is disallowed). Your new example
has
type T *T
which is a recursive type which, while weird, is legal. The important
thing to realise is that the second T in "type T *T" IS NOT
an "int", has nothing to do with "int", does not even necessarily have
the same storage size as "int".
>
> package main
>
> import (
> "fmt"
> )
>
> type T int
>
> func main() {
> var v T
v is effectively an int. On an LP64 platform that's a 32bit variable.
> type T *T
> var w T
w is a pointer to a pointer to a pointer to ... NOT int. On an LP64
platform that's a 64bit variable.
> w = &v
On an LP64 platform &v is a pointer to a 32bit storage, while w is a
pointer to a 64bit storage. There is no surprise that this
assignment does not work.
> *w = v
> fmt.Printf("%T %T\n", v, w)
> }
>
> https://play.golang.org/p/3wos23oim0I
>
> The compiler says
>
> prog.go:13:4: cannot use &v (type *T) as type T in assignment
What the compiler means is
cannot use &v (type *T_declared_outside_of_main_which_is_a_kind_of_int)
as type T_declared_inside_main_which_is_a_type_of_pointer in assignment.
MSB
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Die Frau verändert dich.
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