Challenge 3: A Method That Yields — Solution

def with_timing
  if block_given?
    puts "Starting..."
    yield
    puts "Done!"
  else
    puts "No block given!"
  end
end

with_timing do
  puts "Doing some work..."
end

with_timing

=begin
Output:
Starting...
Doing some work...
Done!
No block given!

Notes:
- block_given? checks whether the current call to with_timing was given a
  block at all, before attempting to yield to it.
- The first call passes a block with do...end, so yield hands control to
  that block's body (the "Doing some work..." line) in between the two
  puts statements inside with_timing.
- The second call passes no block at all — no error is raised, because
  block_given? caught that case and printed a fallback message instead of
  reaching the yield line, which would otherwise raise a LocalJumpError.
=end