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作者：<liubin <AT>huangpuzhuang.com>

2004/11/23

　

    在的一篇关于闭包的文章中（，中文版：），提到了一个例子，主要是用Ruby语言写的，后来网上出现了很多其它语言的版本，本文将各个版本摘录下来，方便大家阅读比较。

1.Ruby

摘自原文

1.

def managers(emps)  return emps.select {|e| e.isManager}end

2.

def highPaid(emps)  threshold = 150  return emps.select {|e| e.salary > threshold}end

3.

def paidMore(amount)  return Proc.new {|e| e.salary > amount}end　

4.

highPaid = paidMore(150)john = Employee.newjohn.salary = 200print highPaid.call(john)

　

2.c# 2.0

摘自：

1.

public List
   
     Managers(List
    
      emps) {  return emps.FindAll(delegate(Employee e) {     return e.IsManager;   }}
    
   

2.

public List
   
     HighPaid(List
    
      emps) {  int threshold = 150;  return emps.FindAll(delegate(Employee e) {     return e.Salary > threshold;   });}
    
   

3.

public Predicate
   
     PaidMore(int amount) {  return delegate(Employee e) {     return e.Salary > amount;   }}
   

4.

Predicate
   
     highPaid = PaidMore(150);Employee john = new Employee();john.Salary = 200;Console.WriteLine(highPaid(john));
   

　

3.Python

摘自：　

直接用lambda函数

1.

def managers(emps): 

    return filter(lambda e: e.isManager, emps) 

2.

def highPaid(emps): 

    threshold = 150     return filter(lambda e: e.salary > threshold, emps) 

3.

def paidMore(amount): 

    return lambda e: e.salary > amount

4.

highPaid = paidMore(150)

john = Employee()john.salary = 200print highPaid(john)

另一种方式，用列表包含（list comprehensions）

1.

def managers(emps): 

    return [e for e in emps if e.isManager]

2.

def highPaid(emps): 

    threshold = 150     return [e for e in emps if e.salary > threshold]

　

提供了另一种避免使用lambda的方法：

def paidMore(amount):  def paidMoreCheck(e):    return e.salary > amount  return paidMoreCheck

 

4.Java

摘自：　

jdk 1.5支持

　

private class FindHighPaidEmployees extends Algorithms {    Constraint highPaidEmployee;    public FindHighPaidEmployess(Constraint constraint) {        this.highPaidEmployee = constraint;    }    public Object call(Object o) {        List emps = (List)o;        return findAll(emps, highPaidEmployee);    }}private class PaidMore implements Constraint {    private int salary;    public PaidMore(int salary) {        this.salary = salary;    }    public boolean test(Object o) {        return ((Integer)o).intValue() > salary;    }}

Closure highPaidFinder = new FindHighPaidEmployees(new PaidMore(150));List highPaidEmployees = highPaidFinder.call(myEmployees);

　

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