gistfile1.rb

.0.0-p247 :074 > class Q
2.0.0-p247 :075?>   def test
2.0.0-p247 :076?>     puts "no block. but you can pass a block to me"
2.0.0-p247 :077?>   end
2.0.0-p247 :078?>   def btest(&block)
2.0.0-p247 :079?>     puts "with block"
2.0.0-p247 :080?>     block.call
2.0.0-p247 :081?>   end
2.0.0-p247 :082?>   def ctest
2.0.0-p247 :083?>     if block_given?
2.0.0-p247 :084?>       yield
2.0.0-p247 :085?>     else
2.0.0-p247 :086 >       puts "no block was passed"
2.0.0-p247 :087?>     end
2.0.0-p247 :088?>   end
2.0.0-p247 :089?> end
 => nil
2.0.0-p247 :090 > Q.new.test
no block. but you can pass a block to me
 => nil
2.0.0-p247 :091 > Q.new.test {puts "test"}
no block. but you can pass a block to me
 => nil
2.0.0-p247 :092 > Q.new.btest {puts "block code"}
with block
block code
 => nil
2.0.0-p247 :093 > Q.new.btest
with block
NoMethodError: undefined method `call' for nil:NilClass
        from (irb):80:in `btest'
        from (irb):93
        from /Users/dtt22/.rvm/gems/ruby-2.0.0-p247@daily_themes/gems/railties-4.0.0/lib/rails/commands/console.rb:90:in `start'
        from /Users/dtt22/.rvm/gems/ruby-2.0.0-p247@daily_themes/gems/railties-4.0.0/lib/rails/commands/console.rb:9:in `start'
        from /Users/dtt22/.rvm/gems/ruby-2.0.0-p247@daily_themes/gems/railties-4.0.0/lib/rails/commands.rb:64:in `<top (required)>'
        from bin/rails:4:in `require'
        from bin/rails:4:in `<main>'
2.0.0-p247 :094 > Q.new.ctest {puts "block code"}
block code
 => nil
2.0.0-p247 :095 > Q.new.ctest
no block was passed
 => nil