How cast type when the original arg is a pointer

Question

So I have this:

v, ok := muxctx.Get(req, "req-body-map").(map[string]interface{})

the problem is that:

muxctx.Get(req, "req-body-map")

returns a pointer. I tried dereferencing the pointer like so:

(*(muxctx.Get(req, "req-body-map"))

but I get this:

Invalid indirect of '(muxctx.Get(req, "req-body-map"))' (type 'interface{}') 

so I suppose since the Get method doesn't return a pointer, then I can't dereference it.

Answer 1

Pretty sure you want something like:

// You really want this to be two variables, lest you go mad.
// OK here is mostly to see whether the value exists or not, which is what
// presumably you're testing for.  Get that out of the way before trying to
// get fancy with type coercion.
//
ptr, ok := muxctx.Get(req, "req-body-map")

... // Do other stuff (like your if test maybe)...

// Now coerce and deref.  We coerce the type inside parens THEN we try to
// dereference afterwards.
//
v := *(ptr.(*map[string]interface{}))

A brief example of this general technique:

package main

import "fmt"

func main() {
    foo := 10
    var bar interface{}
    bar = &foo
    fmt.Println(bar)
    foobar := *(bar.(*int))
    fmt.Println(foobar)
}

$ ./spike
0xc00009e010
10

Finally, be really sure you have the type you want (using reflection if needbe) or risk the program panic'ing on a bad type coercion.