Test ruby yield method for block execution

Whenever I pass a block to a yield method in Ruby I would like to know if the block was actually executed. For instance:

def yield_method(list)
  list.each do |item|
    yield item
  end
end

yield_method(ARGV) { |item|
  print item
}

print "executed"

I would like for the

print "executed"

statement to run only if the block passed to the yield method was executed

Solution

You're going to need to init a variable outside of the block and then set it from within the block, then test that.

executed = false
yield_method(ARGV) do |item|
   executed = true
   # whatever else
end
print "executed" if executed

Or you can modify yield_method to return a value based on whether or not the conditions for the block to be executed were met:

def yield_method(list)
  list.each do |item|
    yield item
  end
  list.any?
end

executed = yield_method(ARGV) { ... }
print "executed" if executed

That said, needing to know whether or not a block was executed smells bad to me - I would instead make your test a test of the conditions that would permit the block to execute (as in the second form), and write your code to semantically reflect that. For example:

def process_argv(list)
  list.each do |item|
    yield item
  end
  list.length
end

args_processed = process_argv(ARGV) { ... }
print "executed" if args_processed > 0

This reflects that in this case, you care about whether there were args to process, rather than whether some block ended up being called. If the block has a side effect that you care about, you should test for that side effect directly, rather than assuming it based on block execution.