Method Parameters to String

Question

1) I have a method

def self.createobj(api_key, amnt, commentstr, orderid, order_creation_date, orderfullfilmentdate)  
.....
end

2) I want to create a error_str of all the parameters passed to this function ...

2.1) Something like

errorstr = "api_key: " + api_key.to_s + " amnt: " + amnt.to_s + " commentstr: " + commentstr.to_s + " orderid: " + orderid.to_s + " order_creation_date: " + order_creation_date.to_s + " orderfullfilmentdate: " + orderfullfilmentdate.to_s

2.2) So I created another method

def self.get_params_str(a)
    str = ""
    a.each do |a|
      str = str + a.to_s
    end
    return str
end

2.3) So I call this new method from createobj. Something like

def self.createobj(api_key, amnt, commentstr, orderid, order_creation_date, orderfullfilmentdate)  
errorstr = get_params_str(args)
.....
end

3) But I get error undefined local variable or method `args' for #. Shouldn't args have all parameters?

Please advice.

Larry K · Accepted Answer · 2011-10-06 17:57:43Z

What you're trying to do (trying to use a magic var called args that will hold all of the arguments) doesn't work in this way in Ruby.

A method can have optional args:

def my_method(*args)
  ....
  # the array args will have 0 or more elements, depending on how many
  # were in the method invocation.
end

But if a method has specific (required) args, as in your example, then there is no other way to get at them.

Added If you're willing to change the definition of your method to use the work-around for named arguments, then the args will arrive as an associative array and you can then send them to your get_params_string

Or better, redefine your get_params_string to take a variable arg list

def self.get_params_str(*a)
  str = ""
  a.each do |a|
    str = str + a.to_s
  end
  return str
end  

# Then call it from your main method:
def self.createobj(api_key, amnt, commentstr, orderid, 
                   order_creation_date, orderfullfilmentdate)  
  errorstr = get_params_str(api_key, amnt, commentstr, orderid, 
                   order_creation_date, orderfullfilmentdate)
  .....
end

See a useful post

Carl Zulauf · Accepted Answer · 2011-10-06 17:53:21Z

1

args would only contain the parameters if your method definition was something like def self.createobj(*args). Without that args isn't defined.

You will need to manually pass all of the parameters to get_params_str. You will need to pass them as an array, i.e get_params_str([api_key, amnt, commentstr, ...]) unless you change get_params_str's method signature to def self.get_params_str(*a) (which puts all of the parameters passed to get_params_str into a single array`).

answered Oct 6, 2011 at 17:53

Carl Zulauf

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Comments

derp · Accepted Answer · 2011-10-06 20:16:54Z

1

As stated in the other responses there's no available variable like args that provides the names of the arguments for the method, however if you're on Ruby 1.9.2 (I can't confirm if exist on 1.9.1 as well) you have the method parameters so you can do something like this:

def foo(a, b, c)
    errorstr = method(:foo).parameters.map{|p| "#{p.last}: #{eval p.last.to_s}" }.join(', ')
    puts errorstr
end

foo(1, 2, 3) #=> a: 1, b: 2, c: 3

answered Oct 6, 2011 at 20:16

derp

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2 Comments

Larry K Over a year ago

+1 So parameters is a reflection of the named parameters? Clever.

derp Over a year ago

I don't know the extent of parameters but for example if you try it on def test(a, *b, &blk) ; end you will get [[:req, :a], [:rest, :b], [:block, :blk]] so not only it gives you the name as a symbol but also tell you if it's required, block, etc.

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