Is there a way to access method arguments in Ruby?

Question

New to Ruby and ROR and loving it each day, so here is my question since I have not idea how to google it (and I have tried :) )

we have method

def f         


        

Answer 1

This may be helpful...

  def foo(x, y)
    args(binding)
  end

  def args(callers_binding)
    callers_name = caller[0][/`.*'/][1..-2]
    parameters = method(callers_name).parameters
    parameters.map { |_, arg_name|
      callers_binding.local_variable_get(arg_name)
    }    
  end

Answer 2

One way to handle this is:

def foo(*args)
    first_name, last_name, age, sex, is_plumber = *args
    # some code
    # error happens here
    logger.error "Method has failed, here are all method arguments #{args.inspect}"    
end

Answer 3

If you would change the method signature, you can do something like this:

def foo(*args)
  # some code
  # error happens here
  logger.error "Method has failed, here are all method arguments #{args}"    
end

Or:

def foo(opts={})
  # some code
  # error happens here
  logger.error "Method has failed, here are all method arguments #{opts.values}"    
end

In this case, interpolated args or opts.values will be an array, but you can join if on comma. Cheers

Answer 4

It seems like what this question is trying to accomplish could be done with a gem I just released, https://github.com/ericbeland/exception_details. It will list local variables and vlaues (and instance variables) from rescued exceptions. Might be worth a look...

Answer 5

In Ruby 1.9.2 and later you can use the parameters method on a method to get the list of parameters for that method. This will return a list of pairs indicating the name of the parameter and whether it is required.

e.g.

If you do

def foo(x, y)
end

then

method(:foo).parameters # => [[:req, :x], [:req, :y]]

You can use the special variable __method__ to get the name of the current method. So within a method the names of its parameters can be obtained via

args = method(__method__).parameters.map { |arg| arg[1].to_s }

You could then display the name and value of each parameter with

logger.error "Method failed with " + args.map { |arg| "#{arg} = #{eval arg}" }.join(', ')

---

Note: since this answer was originally written, in current versions of Ruby eval can no longer be called with a symbol. To address this, an explicit to_s has been added when building the list of parameter names i.e. parameters.map { |arg| arg[1].to_s }