Here's what I have so far: https://play.golang.org/p/X2z7Yl9UPg
I think it works for my purposes. However, I'm confused about one thing: Why does reflect.Value.Set panic when passed a zero-value? On Monday, 7 November 2016 16:56:52 UTC-8, freeformz wrote: > > Then just use pointers (see lines 45+): > https://play.golang.org/p/vl47WDHOdN > > On Mon, Nov 7, 2016 at 4:50 PM Kaylen Wheeler <kfjwh...@gmail.com > <javascript:>> wrote: > >> I want pointers because I want most components to be structs, and I want >> the ability to modify the fields in those structs. >> >> On Monday, 7 November 2016 16:46:17 UTC-8, freeformz wrote: >> >>> Why do you want to use pointers? >>> >>> On Mon, Nov 7, 2016 at 4:42 PM Kaylen Wheeler <kfjwh...@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()]) >>>>> } >>>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "golang-nuts" group. >>>> >>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to golang-nuts...@googlegroups.com. >>> >>> >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
