지연된 초기화

지연된 초기화, 게으른 초기화(lazy initialization)은 컴퓨터 프로그래밍에서 객체 생성, 값 계산, 또는 일부 기타 비용이 많이 드는 과정을 처음 필요한 시점까지 지연시키는 기법이다.

예시

액션스크립트 3 
package examples.lazyinstantiation
{
	public class Fruit
	{
		private var _typeName:String;
		private static var instancesByTypeName:Dictionary = new Dictionary();

		public function Fruit(typeName:String):void
		{
			this._typeName = typeName;
		}

		public function get typeName():String
		{
			return _typeName;
		}

		public static function getFruitByTypeName(typeName:String):Fruit
		{
			return instancesByTypeName[typeName] ||= new Fruit(typeName);
		}

		public static function printCurrentTypes():void
		{
			for each (var fruit:Fruit in instancesByTypeName)
			{
				// iterates through each value
				trace(fruit.typeName);
			}
		}
	}
}
기본 사용법:
package
{
	import examples.lazyinstantiation;

	public class Main
	{
		public function Main():void
		{
			Fruit.getFruitByTypeName("Banana");
			Fruit.printCurrentTypes();

			Fruit.getFruitByTypeName("Apple");
			Fruit.printCurrentTypes();

			Fruit.getFruitByTypeName("Banana");
			Fruit.printCurrentTypes();
		}
	}
}

C 
함수에서:
#include <string.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdio.h>

struct fruit {
    char *name;
    struct fruit *next;
    int number;
    /* Other members */
};

struct fruit *get_fruit(char *name) {
    static struct fruit *fruit_list;
    static int seq;
    struct fruit *f;
    for (f = fruit_list; f; f = f->next)
        if (0 == strcmp(name, f->name))
            return f;
    if (!(f = malloc(sizeof(struct fruit))))
        return NULL;
    if (!(f->name = strdup(name))) {
        free(f);
        return NULL;
    }
    f->number = ++seq;
    f->next = fruit_list;
    fruit_list = f;
    return f;
}

/* Example code */

int main(int argc, char *argv[]) {
    int i;
    struct fruit *f;
    if (argc < 2) {
        fprintf(stderr, "Usage: fruits fruit-name [...]\n");
        exit(1);
    }
    for (i = 1; i < argc; i++) {
        if ((f = get_fruit(argv[i]))) {
            printf("Fruit %s: number %d\n", argv[i], f->number);
        }
    }
    return 0;
}

fruit.h:
#ifndef _FRUIT_INCLUDED_
#define _FRUIT_INCLUDED_

struct fruit {
    char *name;
    struct fruit *next;
    int number;
    /* Other members */
};

struct fruit *get_fruit(char *name);
void print_fruit_list(FILE *file);

#endif /* _FRUIT_INCLUDED_ */

fruit.c:
#include <string.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdio.h>
#include "fruit.h"

static struct fruit *fruit_list;
static int seq;

struct fruit *get_fruit(char *name) {
    struct fruit *f;
    for (f = fruit_list; f; f = f->next)
        if (0 == strcmp(name, f->name))
            return f;
    if (!(f = malloc(sizeof(struct fruit))))
        return NULL;
    if (!(f->name = strdup(name))) {
        free(f);
        return NULL;
    }
    f->number = ++seq;
    f->next = fruit_list;
    fruit_list = f;
    return f;
}

void print_fruit_list(FILE *file) {
    struct fruit *f;
    for (f = fruit_list; f; f = f->next)
        fprintf(file, "%4d  %s\n", f->number, f->name);
}

main.c:
#include <stdlib.h>
#include <stdio.h>
#include "fruit.h"

int main(int argc, char *argv[]) {
    int i;
    struct fruit *f;
    if (argc < 2) {
        fprintf(stderr, "Usage: fruits fruit-name [...]\n");
        exit(1);
    }
    for (i = 1; i < argc; i++) {
        if ((f = get_fruit(argv[i]))) {
            printf("Fruit %s: number %d\n", argv[i], f->number);
        }
    }
    printf("The following fruits have been generated:\n");
    print_fruit_list(stdout);
    return 0;
}

Haxe 
Haxe의 예는 다음과 같다:class Fruit {
  private static var _instances = new Map<String, Fruit>();

  public var name(default, null):String;

  public function new(name:String) {
    this.name = name;
  }

  public static function getFruitByName(name:String):Fruit {
    if (!_instances.exists(name)) {
      _instances.set(name, new Fruit(name));
    }
    return _instances.get(name);
  }

  public static function printAllTypes() {
    trace([for(key in _instances.keys()) key]);
  }
}사용법class Test {
  public static function main () {
    var banana = Fruit.getFruitByName("Banana");
    var apple = Fruit.getFruitByName("Apple");
    var banana2 = Fruit.getFruitByName("Banana");

    trace(banana == banana2); // true. same banana

    Fruit.printAllTypes(); // ["Banana","Apple"]
  }
}

각주 

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