Question

If I run the tests below on this code, it returns

 ALERT: an event that always happens

I expected it to also put

 ALERT: an event that never happens

but it didn’t. I assume the reason for the difference is the ‘true’ and ‘false’ in the respective tests, but I don’t see why ‘true’ or ‘false’ make a difference in this case. The method ‘event’ says

puts "ALERT: #{name}" if yield

If the result of the tests is explained by the fact that ‘true’ equals ‘yield’ in this context, whereas ‘false’ doesn’t, how does ‘false’ negate ‘yield’?

Question: Does ‘if yield’ mean ‘yield if the block evaluates to true’?

code

def event(name)
  puts "ALERT: #{name}" if yield
end

Dir.glob('*events.rb').each {|file| load file }

tests

event "an event that always happens" do
  true                     
end

event "an event that never happens" do
  false                       
end

Output

ALERT: an event that always happens

Answer 1

This might be helpful.

def event(name)
  val = yield
  puts val.inspect
  puts "ALERT: #{name}" if val == "donald"
end

event "an event that always happens" do
  "donald"
end

event "an event that never happens" do
  "duck"
end

prints

"donald"
ALERT: an event that always happens
"duck"

Basically the return value of yield is whatever gets evaluated last in the block. And that is what is being used as a criteria in the if statement.