在 Ruby 中，'new' 和 'initialize' 之间的关系是什么?初始化时如何返回nil? [英] In Ruby, what's the relationship between 'new' and 'initialize'? How to return nil while initializing?

问题描述

我想要的是:

obj = Foo.new(0)  # => nil or false

这不起作用:

class Foo
  def initialize(val)
    return nil if val == 0
  end
end

我知道在 C/C++/Java/C# 中，我们不能在构造函数中返回值.

I know in C/C++/Java/C#, we cant return a value in a constructor.

但我想知道在 Ruby 中是否可行.

But I'm wondering whether it is possible in Ruby.

推荐答案

在 Ruby 中，'new' 和 'initialize' 之间的关系是什么?

In Ruby, what's the relationship between 'new' and 'initialize'?

new 通常调用 initialize.new 的默认实现类似于:

new typically calls initialize. The default implementation of new is something like:

class Class
  def new(*args, &block)
    obj = allocate

    obj.initialize(*args, &block)
    # actually, this is obj.send(:initialize, …) because initialize is private

    obj
  end
end

当然，您可以覆盖它以执行任何您想做的事情.

But you can, of course, override it to do anything you want.

初始化时如何返回nil?

How to return nil while initializing?

我想要的是:

obj = Foo.new(0)  # => nil or false

这不起作用:

class Foo
  def initialize(val)
    return nil if val == 0
  end
end

我知道在 C/C++/Java/C# 中，我们不能在构造函数中返回值.

I know in C/C++/Java/C#, we cant return a value in a constructor.

但我想知道在 Ruby 中是否可行.

But I'm wondering whether it is possible in Ruby.

Ruby 中没有构造函数这样的东西.在 Ruby 中，只有方法，它们可以返回值.

There is no such thing as a constructor in Ruby. In Ruby, there are only methods, and they can return values.

您所看到的问题只是您想更改一个方法的返回值，但您覆盖了另一个方法.如果你想改变方法bar的返回值，你应该覆盖bar，而不是其他方法.

The problem you are seeing is simply that you want to change the return value of one method but you are overriding a different method. If you want to change the return value of method bar, you should override bar, not some other method.

如果你想改变Foo::new的行为，那么你应该改变Foo::new:

If you want to change the behavior of Foo::new, then you should change Foo::new:

class Foo
  def self.new(val)
    return nil if val.zero?
    super
  end
end

但是请注意，这是一个非常糟糕的主意，因为它违反了 new 的约定，即返回一个完全初始化的、功能齐全的班级.

Note, however, that this is a really bad idea, since it violates the contract of new, which is to return a fully initialized, fully functioning instance of the class.

这篇关于在 Ruby 中，'new' 和 'initialize' 之间的关系是什么?初始化时如何返回nil?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！