Does adding a block to Object.send pass it to the called method?

Question

I just completed the Ruby Koans, and neither the unit on calling methods using Object.send nor the Ruby documentation on the method provides any information on using blocks with the send method. Will a block attached to the send method be passed to the method it calls, or will the block be lost?

Example:

foo.send(:a_method) { bar.another_method } 

Answer 1

The documentation is a bit unclear on this:

send(symbol [, args...]) → obj

Invokes the method identified by symbol, passing it any arguments specified.

But note the any arguments specified part. The block that you give to a method is really a funny type of implicit argument so that you can do things like:

def m(&b)   @a.each(&b) end m { |e| puts e } 

to pass the block around as a Proc instance. However, you can also do this:

def m   yield end m { puts 'pancakes' } 

so the block is special as far as the argument list is concerned but the block still behaves as an argument even if it is sometimes implicit.

Given the above "block is sort of an argument" rambling and the importance of blocks in Ruby, it would be reasonable for send to pass the block through. You can also try it but you have to careful about accidental and undocumented behavior with the "try it" approach:

class C   def m     yield   end end o = C.new o.send(:m) { puts 'pancakes' } # "pancakes" comes out 

Answer 2

Yes. Consider the following:

class A   def explicit(&b); b; end   def implicit; yield "hello"; end end  >> A.new.send(:explicit) { } => #<Proc:0x0000000000000000@(irb):19> >> A.new.send(:implicit) { |greeting| puts greeting } hello => nil 

Hope this helps!