如何将块转发到生成方法的方法

Question

在我当前的项目中，我在一些类中有以下重复模式：

class MyClass

  def method1(pars1, ...)
    preamble

    # implementation method1

    rescue StandardError => e
      recovery
  end

  def method2(pars2, ...)
    preamble

    # implementation method2

    rescue StandardError => e
      recovery
  end

  # more methods with the same pattern
end

所以，我一直在思考如何干掉那个重复的图案。我的目标是拥有这样的东西：

class MyClass

  define_operation :method1, pars1, ... do
    # implementation method1
  end

  define_operation :method2, pars2, ... do
    # implementation method2
  end

  # more methods with the same pattern but generated with define_wrapper_method
  end

我曾尝试实现一种元生成器，但在转发接收生成器的块时遇到了问题。这或多或少是我尝试过的：

def define_operation(op_name, *pars, &block)
  define_method(op_name.to_s) do |*pars|
    preamble
    yield # how can I do here for getting the block? <-----
    rescue StandardError => e
      recovery
  end
end

不幸的是，我找不到将 block 转发到 define_method 方法的方法。此外，很可能参数的数量是可变的，以错误的方式传递给 define_method。

如果有任何线索、帮助、建议，我将不胜感激。

Answer 1

您不需要元编程来实现这一点。只需添加一个包装通用逻辑的新方法，如下所示：

class MyClass

  def method1(param1)
    run_with_recovery(param1) do |param1|
       # implementation method1
    end
  end

  def method2(param1, param2)
    run_with_recovery(param1, param2) do |param1, param2|
       # implementation method2
    end
  end

  private

  def run_with_recovery(*params)
    preamble
    yield(*params)
    rescue StandardError => e
      recovery
  end
end

在这里测试：http://rubyfiddle.com/riddles/4b6e2

如果您真的想进行元编程，这会起作用：

class MyClass

  def self.define_operation(op_name)
    define_method(op_name.to_s) do |*args|
      begin
        puts "preamble"
        yield(args)
      rescue StandardError => e
        puts "recovery"
      end
    end
  end

  define_operation :method1 do |param1|
    puts param1
  end

  define_operation :method2 do |param1, param2|
    puts param1
    puts param2
  end

end

MyClass.new.method1("hi")
MyClass.new.method2("hi", "there")

在此处测试：http://rubyfiddle.com/riddles/81b9d/2

Answer 2

如果我理解正确的话，您正在寻找类似的东西：

class Operation
  def self.op(name,&block)
    define_method(name) do |*args|
      op_wrap(block.arity,*args,&block)
    end
  end

  def op_wrap(arity=0,*args)
    if arity == args.size || (arrity < 0  && args.size >= arity.abs - 1) 
      begin
        preamble 
        yield *args
      rescue StandardError => e
        recovery 
      end  
    else 
      raise ArgumentError, "wrong number of arguments (given #{args.size}, expected #{arity < 0 ? (arity.abs - 1).to_s.+('+') : arity })"
    end
  end

  def preamble
    puts __method__
  end

  def recovery
    puts __method__
  end
end

所以你的用法是

class MyClass < Operation

  op :thing1 do |a,b,c| 
    puts "I got #{a},#{b},#{c}"
  end

  op :thing2 do |a,b|
    raise StandardError
  end

  def thing3
    thing1(1,2,3) 
  end
end

此外，这为您提供了两个选项，您仍然可以这样做

def thing4(m1,m2,m3) 
   @m1 = m1
   op_wrap(1,'inside_wrapper') do |str| 
     # no need to yield because the m1,m2,m3 are in scope 
     # but you could yield other arguments
     puts "#{str} in #{__method__}" 
   end
end

允许您预处理参数并决定将什么交给块

例子

m = MyClass.new

m.thing1(4,5,6)
# preamble
# I got 4,5,6
#=> nil
m.thing2('A','B')
# preamble
# recovery
#=> nil
m.thing3  
# preamble
# I got 1,2,3
#=> nil
m.thing1(12)
#=> #<ArgumentError: wrong number of arguments (given 1, expected 3)>

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