Ruby：获取变量名称

参见英文答案 > Ruby – print the variable name and then its value8个
我如何获得变量名称？例如.,

def get_var_name(var)
  # return variable name
end

myname = nil
get_var_name myname #=> myname

初衷：

somevar = "value"

puti somevar #=> somevar = "value"
# that is a shortage for
# `puts "somevar = #{somevar.inspect}"`

我的尝试：

def puti(symb)
  var_name  = symb.to_s
  var_value = eval(var_name)
  puts "#{var_name} = #{var_value.inspect}"
end
puti :@somevar # that actually will work only with class vars or whatever considering var scope;

解决方法

首先,你不能实现puti并直接调用puti a_var来获得输出a_var = a_var的值.在puti的主体,Ruby只看到puti的形式参数名称,它无法推断出实际的参数名称.

在其他语言如C/C++中,您可以使用Macro来实现您的puti.那是另一个故事.

但是,您可以在Continuation的帮助下实现put：a_var.在另一个问题“Can you eval code in the context of a caller in Ruby?”中,Sony Santos提供了一个caller_binding实现来获取调用者的绑定(类似于perl调用函数).

实现应该稍微改变一下,因为callcc在第一次返回时返回块的返回值.因此,您将获得Continuation的实例而不是nil.这是更新版本：

require 'continuation' if RUBY_VERSION >= '1.9.0'

def caller_binding
  cc = nil     # must be present to work within lambda
  count = 0    # counter of returns

  set_trace_func lambda { |event,file,lineno,id,binding,klass|
    # First return gets to the caller of this method
    # (which already know its own binding).
    # Second return gets to the caller of the caller.
    # That's we want!
    if count == 2
      set_trace_func nil
      # Will return the binding to the callcc below.
      cc.call binding
    elsif event == "return"
      count += 1
    end
  }
  # First time it'll set the cc and return nil to the caller.
  # So it's important to the caller to return again
  # if it gets nil,then we get the second return.
  # Second time it'll return the binding.
  return callcc { |cont| cc = cont; nil }
end

# Example of use:

def puti *vars
  return unless bnd = caller_binding
  vars.each do |s|
    value = eval s.to_s,bnd
    puts "#{s} = #{value.inspect}"
  end
end

a = 1
b = 2
puti :a,:b
e = 1 # place holder...

# => a = 1
#    b = 2

请注意,puti不应该是程序的最后一个语句,否则ruby解释器将立即终止并且跟踪功能无法运行.这就是最后一个“占位符”行的重点.

原文链接：https://www.f2er.com/ruby/270684.html

Ruby：获取变量名称

解决方法

猜你在找的Ruby相关文章