How do I access a map keyword using reflection?

Question

I have a null key card:

mapp := map[interface{}]interface{}{
    nil: "a",
}

Accessing it nil key directly works:

fmt.Println("key[nil]:", mapp[nil])

But with reflection this is not the case - how to do it?

rmapp := reflect.ValueOf(mapp)
rkey := reflect.ValueOf(interface{}(nil))
rval := rmapp.MapIndex(rmapp.MapIndex(rkey))
fmt.Println("key[nil]:", rval)

The broken code is here:
https://play.golang.org/p/6TKN_tDNgV

+3

go

Gima 07 jan. 15 at 14:38

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2 answers

Here's one way to create a value reflect.Value

for a nil

type interface{}

:

rkey := reflect.ValueOf(new(interface{})).Elem()

playground example

+5

ThunderCat 07 jan. 15:03 pm

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Gima · Accepted Answer · 2015-01-07T17:41:55+0000

The missing element appears to have been a null value of the map key type, which is required to access the nil key on the map.

refmap.MapIndex(reflect.Zero(refmap.Type().Key()))

playground example