Get: Should return typed nil when out is nil/empty slice

[mattayes]

I'm running into an issue when using Get() with a zero-value or empty slice of structs.

Here's an example:

package main

import (
	"fmt"
	"log"

	"github.com/thoas/go-funk"
)

type BigThing struct {
	Littles []LittleThing
}

type LittleThing struct {
	SomeKey string
}

func main() {
	// Using a zero-value slice (unexpected output)
	var x BigThing
	iKeys := funk.Get(x.Littles, "SomeKey")
	if _, ok := iKeys.([]string); ok {
		log.Fatalf("Uh oh...")
	}
	fmt.Printf("iKeys is %T, not []string\n", iKeys)

	// Using an empty slice (unexpected output)
	x.Littles = []LittleThing{}
	iKeys = funk.Get(x.Littles, "SomeKey")
	if _, ok := iKeys.([]string); ok {
		log.Fatalf("Uh oh...")
	}
	fmt.Printf("iKeys is %T, not []string\n", iKeys)

	// Using a non-empty slice (expected output)
	x.Littles = []LittleThing{{SomeKey: "hello"}}
	iKeys = funk.Get(x.Littles, "SomeKey")
	keys, ok := iKeys.([]string)
	if !ok {
		log.Fatalf("Uh oh...")
	}
	fmt.Println(keys)
}

I expected all three cases to return a zero-value []string (i.e., a typed nil), however the first two return an untyped nil, which causes these type conversions to fail.

[mattayes]

Thanks @vellotis! Thanks @thoas!