pointer_indirection.go

package main

import (
	"container/list"
	"fmt"
	"time"
)

func main() {
	l := list.New()
	now := time.Now()
	l.PushFront(now)

	// Here's where the problem begins. When you fetch the first item,
	// you get an `Element`, not the value you pushed. It's a struct with
	// a single external field, `Value interface{}`.
	front := l.Front()

	// This code doesn't work & blows up.
	// """front.Value.Year undefined (type interface {} has no field or method Year)"""
	// fmt.Print(front.Value.Year())

	// I tried a type assertion, to fix what the compiler grumped about.
	// But somehow messed this up, because at the time I was storing a pointer to `now` in the list, rather than... the value?
	// t := front.Value.(time.Time)
	// In retrospect, this is the same as the solution below & IDFK.

	// Tried to cast it as a pointer failed.
	// var grump *time.Time
	// t, ok : = front.Value.(time.Time)
	// grump = (*time.Time)(t)
	// Still kaboom: """cannot convert t (type time.Time) to type *time.Time"""
	// fmt.Print(t.Year())

	// Eventually, after an hour or so of source-diving & searching, I
	// tried this, which (spoiler alert) works:
	if t, ok := front.Value.(time.Time); ok {
		fmt.Print(t.Year())
	}
}