Question

我在Ruby中有一个像这样工作的DSL：

desc 'list all todos'
command :list do |c|
  c.desc 'show todos in long form'
  c.switch :l
  c.action do |global,option,args|
    # some code that's not relevant to this question
  end
end

desc 'make a new todo'
command :new do |c|
  # etc.
end

一位开发人员建议我将我的DSL增强为不需要将c传递到command块，因此不需要所有c. 里面的方法;据推测，他暗示我可以使下面的代码工作相同：

desc 'list all todos'
command :list do
  desc 'show todos in long form'
  switch :l
  action do |global,option,args|
    # some code that's not relevant to this question
  end
end

desc 'make a new todo'
command :new do
  # etc.
end

command的代码类似于

def command(*names)
  command = make_command_object(..)
  yield command                                                                                                                      
end

我尝试了几件事而无法让它发挥作用;我无法弄清楚如何将command块中的代码的上下文/绑定更改为与默认值不同。

关于这是否可能以及我如何做的任何想法？

Answer 1

粘贴此代码：

  def evaluate(&block)
    @self_before_instance_eval = eval "self", block.binding
    instance_eval &block
  end

  def method_missing(method, *args, &block)
    @self_before_instance_eval.send method, *args, &block
  end

有关详情，请参阅这篇非常好的文章here

Answer 2

也许

def command(*names, &blk)
  command = make_command_object(..)
  command.instance_eval(&blk)
end

可以在命令对象的上下文中评估块。

Answer 3

class CommandDSL
  def self.call(&blk)
    # Create a new CommandDSL instance, and instance_eval the block to it
    instance = new
    instance.instance_eval(&blk)
    # Now return all of the set instance variables as a Hash
    instance.instance_variables.inject({}) { |result_hash, instance_variable|
      result_hash[instance_variable] = instance.instance_variable_get(instance_variable)
      result_hash # Gotta have the block return the result_hash
    }
  end

  def desc(str); @desc = str; end
  def switch(sym); @switch = sym; end
  def action(&blk); @action = blk; end
end

def command(name, &blk)
  values_set_within_dsl = CommandDSL.call(&blk)

  # INSERT CODE HERE
  p name
  p values_set_within_dsl 
end

command :list do
  desc 'show todos in long form'
  switch :l
  action do |global,option,args|
    # some code that's not relevant to this question
  end
end

将打印：

:list
{:@desc=>"show todos in long form", :@switch=>:l, :@action=>#<Proc:0x2392830@C:/Users/Ryguy/Desktop/tesdt.rb:38>}

Answer 4

我写了一个处理这个问题的类，并处理@instance_variable访问，嵌套等等。这是另一个问题的写作：

Block call in Ruby on Rails

在ruby中更改块内的上下文/绑定

4 个答案: