How do you pass arguments to define_method?

Question

I would like to pass an argument(s) to a method being defined using define_method, how would I do that?

Answer 1

... and if you want optional parameters

 class Bar
   define_method(:foo) do |arg=nil|                  
     arg                                                                                          
   end   
 end

 a = Bar.new
 a.foo
 #=> nil
 a.foo 1
 # => 1

... as many arguments as you want

 class Bar
   define_method(:foo) do |*arg|                  
     arg                                                                                          
   end   
 end

 a = Bar.new
 a.foo
 #=> []
 a.foo 1
 # => [1]
 a.foo 1, 2 , 'AAA'
 # => [1, 2, 'AAA']

...combination of

 class Bar
   define_method(:foo) do |bubla,*arg|
     p bubla                  
     p arg                                                                                          
   end   
 end

 a = Bar.new
 a.foo
 #=> wrong number of arguments (0 for 1)
 a.foo 1
 # 1
 # []

 a.foo 1, 2 ,3 ,4
 # 1
 # [2,3,4]

... all of them

 class Bar
   define_method(:foo) do |variable1, variable2,*arg, &block|  
     p  variable1     
     p  variable2
     p  arg
     p  block.inspect                                                                              
   end   
 end
 a = Bar.new      
 a.foo :one, 'two', :three, 4, 5 do
   'six'
 end

Update

Ruby 2.0 introduced double splat ** (two stars) which (I quote) does:

Ruby 2.0 introduced keyword arguments, and ** acts like *, but for keyword arguments. It returns a Hash with key / value pairs.

...and of course you can use it in define method too :)

 class Bar 
   define_method(:foo) do |variable1, variable2,*arg,**options, &block|
     p  variable1
     p  variable2
     p  arg
     p  options
     p  block.inspect
   end 
 end 
 a = Bar.new
 a.foo :one, 'two', :three, 4, 5, ruby: 'is awesome', foo: :bar do
   'six'
 end
# :one
# "two"
# [:three, 4, 5]
# {:ruby=>"is awesome", :foo=>:bar}

Named attributes example:

 class Bar
   define_method(:foo) do |variable1, color: 'blue', **other_options, &block|
     p  variable1
     p  color
     p  other_options
     p  block.inspect
   end
 end
 a = Bar.new
 a.foo :one, color: 'red', ruby: 'is awesome', foo: :bar do
   'six'
 end
# :one
# "red"
# {:ruby=>"is awesome", :foo=>:bar}

I was trying to create example with keyword argument, splat and double splat all in one:

 define_method(:foo) do |variable1, variable2,*arg, i_will_not: 'work', **options, &block|
    # ...

or

 define_method(:foo) do |variable1, variable2, i_will_not: 'work', *arg, **options, &block|
    # ...

... but this will not work, it looks like there is a limitation. When you think about it makes sense as splat operator is "capturing all remaining arguments" and double splat is "capturing all remaining keyword arguments" therefore mixing them would break expected logic. (I don't have any reference to prove this point doh! )

update 2018 August:

Summary article: https://blog.eq8.eu/til/metaprogramming-ruby-examples.html