Detecting default parameters

ruby-talk
1

Ian Macdonald wrote:

Hello,

Does anyone know of a way to detect whether default parameters are
beingused in a method? I’m looking for something like the pseudo-
method’default?’ in the following example:

def my_method(foo=‘bar’)
if foo.default?
puts “warning: default value #{foo} being used for ‘foo’”
end
end

I suspect Ruby no longer holds any state at this point to reflect the
fact that the caller did not supply a parameter, but I’m hoping
there’ssome way to do it.

Try this:

#!/usr/bin/ruby

class Object
def default?
false
end
end

def default(obj)
defparam = obj.clone

class << defparam
	def default?
		true
	end
end

defparam

end

def foo(bar=(default ‘foo’))
if bar.default?
puts “default”
else
puts “custom”
end

puts bar

end

foo ‘baz’
foo

This might be as close as you’ll get. It doesn’t work for everything, though, since you can’t clone everything, and I don’t want to redefine #default? on things you can’t clone (like Fixnums) since that’d make things wrong.

  • Dan
2

Daniel Doel wrote:

Ian Macdonald wrote:

Hello,

Does anyone know of a way to detect whether default parameters are
beingused in a method? I’m looking for something like the pseudo-
method’default?’ in the following example:

def my_method(foo=‘bar’)
if foo.default?
puts “warning: default value #{foo} being used for ‘foo’”
end
end

I suspect Ruby no longer holds any state at this point to reflect the
fact that the caller did not supply a parameter, but I’m hoping
there’ssome way to do it.

Try this:

#!/usr/bin/ruby

class Object
def default?
false
end
end

def default(obj)
defparam = obj.clone

class << defparam
def default?
true
end
end

defparam
end

def foo(bar=(default ‘foo’))
if bar.default?
puts “default”
else
puts “custom”
end

puts bar
end

foo ‘baz’
foo

This might be as close as you’ll get. It doesn’t work for everything, though, since you can’t clone everything, and I don’t want to redefine #default? on things you can’t clone (like Fixnums) since that’d make things wrong.

  • Dan

Interesting. It seems like you could use SimpleDelegator here:

require ‘delegate’
def default(obj)
defparam = SimpleDelegator.new(obj)
class << defparam
def default?
true
end
end
defparam
end