add tag v2_2_9

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/tags/v2_2_9@61257 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 107 insertions, 0 deletions

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+= Miscellaneous Syntax
+
+== Ending an Expression
+
+Ruby uses a newline as the end of an expression.  When ending a line with an
+operator, open parentheses, comma, etc. the expression will continue.
+
+You can end an expression with a <code>;</code> (semicolon).  Semicolons are
+most frequently used with <code>ruby -e</code>.
+
+== Indentation
+
+Ruby does not require any indentation.  Typically ruby programs are indented
+two spaces.
+
+If you run ruby with warnings enabled and have an indentation mis-match you
+will receive a warning.
+
+== +alias+
+
+The +alias+ keyword is most frequently used to alias methods.  When aliasing a
+method you can use either its name or a symbol:
+
+  alias new_name old_name
+  alias :new_name :old_name
+
+For methods, Module#alias_method can often be used instead of +alias+.
+
+You can also use +alias+ to alias global variables:
+
+  $old = 0
+
+  alias $new $old
+
+  p $new # prints 0
+
+You may use +alias+ in any scope.
+
+== +undef+
+
+The +undef+ keyword prevents the current class from responding to calls to the
+named methods.
+
+  undef my_method
+
+You may use symbols instead of method names:
+
+  undef :my_method
+
+You may undef multiple methods:
+
+  undef method1, method2
+
+You may use +undef+ in any scope.  See also Module#undef_method
+
+== +defined?+
+
++defined?+ is a keyword that returns a string describing its argument:
+
+  p defined?(UNDEFINED_CONSTANT) # prints nil
+  p defined?(RUBY_VERSION)       # prints "constant"
+  p defined?(1 + 1)              # prints "method"
+
+You don't need to use parenthesis with +defined?+ but they are recommended due
+to the {low precedence}[rdoc-ref:syntax/precedence.rdoc] of +defined?+.
+
+For example, if you wish to check if an instance variable exists and that the
+instance variable is zero:
+
+  defined? @instance_variable && @instance_variable.zero?
+
+This returns <code>"expression"</code> which is not what you want if the
+instance variable is not defined.
+
+  @instance_variable = 1
+  defined?(@instance_variable) && @instance_variable.zero?
+
+Adding parentheses when checking if the instance variable is defined is a
+better check.  This correctly returns +nil+ when the instance variable is not
+defined and +false+ when the instance variable is not zero.
+
+Using the specific reflection methods such as instance_variable_defined? for
+instance variables or const_defined? for constants is less error prone than
+using +defined?+.
+
+== +BEGIN+ and +END+
+
++BEGIN+ defines a block that is run before any other code in the current file.
+It is typically used in one-liners with <code>ruby -e</code>.  Similarly +END+
+defines a block that is run after any other code.
+
++BEGIN+ must appear at top-level and +END+ will issue a warning when you use it
+inside a method.
+
+Here is an example:
+
+  BEGIN {
+    count = 0
+  }
+
+You must use <code>{</code> and <code>}</code> you may not use +do+ and +end+.
+
+Here is an example one-liner that adds numbers from standard input or any files
+in the argument list:
+
+  ruby -ne 'BEGIN { count = 0 }; END { puts count }; count += gets.to_i'
+