This was also my swag at an example: https://play.golang.org/p/QG7g9veKEI
PS: it's still not strictly "type safe".
On Mon, Nov 7, 2016 at 4:46 PM Edward Muller <edwar...@interlix.com> wrote:
> Why do you want to use pointers?
>
> On Mon, Nov 7, 2016 at 4:42 PM Kaylen Wheeler <kfjwhee...@gmail.com>
> wrote:
>
> Thanks for the "basic pattern" example here. There's one little
> modification I'm wondering about.
>
> Can this line:
>
> rv.Elem().Set(m[rv.Type()])
>
> be changed to this?
>
> rv.Elem().Set(*&*m[rv.Type()])
>
> If so, how can we check that the input value is a pointer to a pointer.
>
> Or alternatively, is it better that the values in m should be pointers?
>
>
> On Monday, 7 November 2016 16:01:53 UTC-8, adon...@google.com wrote:
>
> On Monday, 7 November 2016 17:55:57 UTC-5, Kaylen Wheeler wrote:
>
> I'm trying to find a typesafe way to access a type-indexed map of
> components. This map can contain objects of any type, and the keys are
> reflect.Type.
>
> One strategy I thought may work would be to pass a pointer to a pointer as
> an out-var. Using reflection to determine the pointer's type, it could be
> populated with a corresponding value.
>
> For instance, if we did something like this:
>
> c := ComponentCollection{}
> c.addComponent(123) // Add an int component
>
> var p : *int
> c.getComponent(&p)
>
>
> In this case, p would point to the int component of c.
>
> That's wht the 2 levels of indirection are necessary: it's an out-var to a
> pointer.
>
> Does that make sense?
>
>
> Here's the basic pattern:
>
> var m = make(map[reflect.Type]reflect.Value)
>
> func addComponent(x interface{}) {
> v := reflect.ValueOf(x)
> m[v.Type(x)] = v
> }
>
> func getComponent(ptr interface{}) {
> rv := reflect.ValueOf(ptr)
> if rv.Kind() != reflect.Pointer {
> panic("not a pointer")
> }
> rv.Elem().Set(m[rv.Type()])
> }
>
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