nil and len() in Go

nil_len.go

package main

import (
	"fmt"
)

type Foo struct{}

func main() {
	var nilPtr *Foo

	var sliceVar []string
	emptySlice := []string{}
	madeSlice := make([]string, 0)
	var slicePtrs []*Foo

	emptyMap := map[string]interface{}{}
	madeMap := make(map[string]interface{})

	fmt.Printf("nilPtr == nil ? %+v\n", nilPtr == nil)
	fmt.Printf("sliceVar == nil ? %+v\n", sliceVar == nil)
	fmt.Printf("emptySlice == nil ? %+v\n", emptySlice == nil)
	fmt.Printf("madeSlice == nil ? %+v\n", madeSlice == nil)
	fmt.Printf("slicePtrs == nil ? %+v\n", slicePtrs == nil)
	fmt.Printf("emptyMap == nil ? %+v\n", emptyMap == nil)
	fmt.Printf("madeMap == nil ? %+v\n", madeMap == nil)

	fmt.Printf("len(sliceVar): %+v\n", len(sliceVar))
	fmt.Printf("len(emptySlice): %+v\n", len(emptySlice))
	fmt.Printf("len(madeSlice): %+v\n", len(madeSlice))
	fmt.Printf("len(emptyMap): %+v\n", len(emptyMap))
	fmt.Printf("len(madeMap): %+v\n", len(madeMap))
	fmt.Printf("len(slicePtrs): %+v\n", len(slicePtrs))
}