difference of block parameter

send_with_block.rb

class Foo
  def block
    yield if block_given?
  end
  def call &b
    b.call if b
  end
end

Foo.new.send(:block) { 'block called' } # => "block called"

l = ->{ 'lambda called' }
Foo.new.send(:call) &l                  # => false
Foo.new.send(:call, &l)                 # => "lambda called"