## mark a section (Learn more)

puts "\nWays of creating a basic block:" def pass_me_a_block_please yield end pass_me_a_block_please { puts "* Put it in brackets." } pass_me_a_block_please { puts "* In curly brackets, all on one line!" } pass_me_a_block_please do puts "* Ooh. You're using 'do' to create a block." end puts "\nWhat happens if you don't pass a block?" begin pass_me_a_block_please rescue LocalJumpError puts "* Oops! Calling yield without passing a block raises a LocalJumpError" end puts "\nYou can use block_given? to test if a block has been passed." def pass_me_a_block_if_you_want_to if block_given? puts "* If you can read this, you DID pass a block, and it's about to be evaluated:" yield else puts "* If you can read this, you didn't pass in a block." end end puts "About to not pass a block!" pass_me_a_block_if_you_want_to # This is okay puts "About to pass a block!" pass_me_a_block_if_you_want_to { # So is this! puts "* If you can read this, the block you just passed has been evaluated!" } puts "\nYou can also just rescue the error if you don't pass in a block:" def pass_me_a_block_if_you_want_to begin yield rescue LocalJumpError puts "* You didn't pass a block, but at least you rescued the error." end end pass_me_a_block_if_you_want_to puts "\nLet's write a method with arguments AND a block!" def pass_me_some_args(arg1, arg2) puts arg1 puts arg2 yield end pass_me_some_args("one", "two") { puts "three" } puts "\nAn ampersand before the last method argument means it's a block." def pass_me_some_args_with_named_block_arg(arg1, arg2, &arg3) puts "\npass_me_some_args_with_named_block_arg" puts arg1 puts arg2 if arg3 # You can also test for a block like this if you have named it. puts "You passed a block named arg3 which is about to be evaluated:" yield else puts "No block passed." end end pass_me_some_args_with_named_block_arg("one", "two") pass_me_some_args_with_named_block_arg("one", "two") { puts "three" } puts "\nWhat about variable scope?" i_am_a_variable_already_defined = "defined_before_the_block_is_called" pass_me_a_block_please { i_am_a_variable_already_defined = "i_can_be_changed_within_a_block" } puts "i_am_a_variable_already_defined: #{i_am_a_variable_already_defined}" pass_me_a_block_please { i_am_just_a_local_variable = "the_answer_to_life_the_universe_and_everything" } begin puts "i_am_just_a_local_variable: #{i_am_just_a_local_variable}" rescue NameError puts "we'll never know what was in i_am_just_a_local_variable" end def change_variable_in_the_method i_am_a_variable_local_to_this_method = "you_cant_change_me_in_the_block_about_to_be_called" yield puts "i_am_a_variable_local_to_this_method: #{i_am_a_variable_local_to_this_method}" end change_variable_in_the_method { i_am_a_variable_local_to_this_method = "this won't change anything!!" } begin puts "i_am_a_variable_local_to_this_method: #{i_am_a_variable_local_to_this_method}" rescue NameError puts "I told you it was just local to that method!" end

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