Question

Suppose we have n constants like:

FOO = 'foo'
BAR = 'bar'
...

I need to check in the block if they exists and are non empty.

%w(FOO BAR FOOBAR).each {|i|
  # this doesn't work
  fail "#{i} is missing or empty" if (! defined?(i) || i.empty?)
}

Answer 1

This is the best way, in my opinion:

[:FOO, :BAR, :FOOBAR].each do |i|
    raise "constant #{i} not defined" unless Object.const_defined?(i)

    puts "constant #{i} exists and has value #{Object.const_get(i)}"
end

EDIT:

Things are a bit more complicated if you want to look up constants in a scope sensitive way (i.e not just top-level constants):

def const_receiver
    is_a?(Module) ? self : class << self; self; end
end

[:FOO, :BAR, :FOOBAR].each do |i|
    raise "constant #{i} not defined" unless const_receiver.const_defined?(i)

    puts "constant #{i} exists and has value #{const_receiver.const_get(i)}"
end