获取块参数的数量

时间:2009-07-03 03:37:45

标签: ruby methods

我需要获取给定块所需的参数数量。例如:

foobar(1,2,3) { |a, b, c|
}

def foobar(x, y, z, &block)
  # need to obtain number of arguments in block
  # which would be 3 in this example
end

这可以在1.9主干中使用,但不能在任何正式版本中使用。我希望如果有任何方法可以做到这一点,而无需下载单独的gem /扩展模块。

2 个答案:

答案 0 :(得分:29)

当您使用&实现块时,它将成为Proc对象,其具有arity方法。要小心 - 如果proc采用* splat arg,它会返回一个补码。

def foobar(x, y, z, &block)
  p block.arity
end

(通过“Ruby编程语言”一书回答。)

答案 1 :(得分:8)

这就是你要找的......

def foobar(x, y, z, &block)
  # need to obtain number of arguments in block
  # which would be 3 in this example
  case block.arity
    when 0 
      yield "i have nothing"
    when 1
      yield "I got ONE block arg"
    when 2
      yield "I got TWO block args"
    when 3
      yield "I got THREE block args"
  end
end

foobar(1,2,3) { |a, b, c|
    puts a
}

输出:

D:\ruby\bin>ruby -v
ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32]

D:\ruby\bin>ruby c:\Temp.rb
I got THREE block args

另见codahale.com的A Ruby HOWTO: Writing A Method That Uses Code Blocks