闭包（Closures）在各种语言中的例子 http://blog.csdn.net/ruby_cn/archive/2004/11/23/192588.aspx

作者：<liubin <AT>huangpuzhuang.com>

http://www.ruby-cn.org/

2004/11/23

　

    在Martin Fowler的一篇关于闭包的文章中（http://martinfowler.com/bliki/Closures.html，中文版：http://www.ruby-cn.org/articles/closures.html），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http://martinfowler.com/bliki/Closures.html

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：http://joe.truemesh.com/blog//000390.html

1.

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

2.

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

3.

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

4.

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

　

3.Python

摘自：http://ivan.truemesh.com/archives/000392.html　

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 = 200
print 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]

　

Chris Reedy 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：　http://joe.truemesh.com/blog//000390.html

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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