Blocks become of class Proc in a useful context ;)

blocks_are_procs.rb

class Proc
  def foobar
    puts "...method on Proc!"
  end  
end  

def block_class &block
  block.call
  block.foobar
  puts block.class.inspect
end  

block_class { puts "I'm a..." }
# I'm a...
# method on Proc!
# Proc

Ruby cheats, actually. It's not a block after it gets passed into the block_class method... but as a block, it has no class.

How is that any different than a method then? Note: I'm only investigating empirically :).

(def foo; end).class #=> NilClass
def block_class(&block)
puts block.inspect
end
block_class {}.class.inspect # => "NilClass"

Try this instead:

def foo(&block)
  block.class.name
end

foo { 1 } # => "Proc"

Of course, you can't just assign a block to a variable without a method. But if you have that method return the block, it is a Proc. So how are blocks not of class Proc?

blocks are of type rb_block_t while procs are an rb_proc_t, which, as you can see, contains an rb_block_t.