如何在Ruby中将一个块传递给另一个? [英] How to pass a block to another in Ruby?

问题描述

假设我有以下操作:

a = Proc.new do
    puts "start"
    yield
    puts "end"
end

还假设我将a传递给另一个方法，该方法随后使用该块在另一个类上调用instance_eval，那么现在如何将一个块传递给该方法的末尾，该方法在a中产生.

Also assuming I pass a to another method which subsequently calls instance_eval on another class with that block, how can I now pass a block onto the end of that method which gets yielded in a.

例如:

def do_something(a,&b)
    AnotherClass.instance_eval(&a) # how can I pass b to a here?
end

a = Proc.new do
    puts "start"
    yield
    puts "end"
end

do_something(a) do
    puts "this block is b!"
end

输出当然应该是:

start
this block is b!
end

如何将辅助块传递给instance_eval中的a?

How can I pass the secondary block to a in the instance_eval?

我需要这样的东西作为我正在工作的Ruby模板系统的基础.

I need something like this for the basis of a Ruby templating system I'm working on.

推荐答案

您不能在a中使用yield.相反，您必须传递Proc对象.这将是新代码:

You can't use yield in a. Rather, you have to pass a Proc object. This would be the new code:

def do_something(a,&b)
    AnotherClass.instance_exec(b, &a)
end

a = Proc.new do |b|
    puts "start"
    b.call
    puts "end"
end

do_something(a) do
    puts "this block is b!"
end

yield仅用于方法.在此新代码中，我使用了instance_exec(Ruby 1.9中的新增功能)，它允许您将参数传递给块.因此，我们可以将Proc对象b作为参数传递给a，该对象可以使用Proc#call()进行调用.

yield is only for methods. In this new code, I used instance_exec (new in Ruby 1.9) which allows you to pass parameters to the block. Because of that, we can pass the Proc object b as a parameter to a, which can call it with Proc#call().

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