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Tech Stuff - Ruby Glossary A - D

The beginning of our point and click glossary to ruby. If the item below has got a link read it - otherwise put up with our definition. You have been warned!

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Symbols ?, #, ::, etc. | a - d | e - l | m - r | s - z

term parent description
access control Core API public, protected, private
# either use as section separator (no parameter)
# terminate section with 'end'

# OR with symbol parameter
# must come AFTER the method definition
public :method1, :method2 # etc
protected :method3, :method4 # etc
private :method5, :method6 # etc
# for Class methods use
accessors Core API (class Module) Ruby uses the term accessors to access what are sometimes called class attributes and provides shortcut syntax to define them:
attr_reader :thing #get only
attr_writer :thing #set only
attr_accessor :thing #get and set 
attr: thing [,true] # short form of attr_accessor

# the last form with the optional [,true] is meant to indicate
# it provides attr_accessor proeprties otherwise attr_reader
# properties - testing suggests this is not the case and 
# that in all cases attr_accessor characteristics are provided.

# OR roll-your-own 
def thing # get
 do something  # compute response OR
 @thing # return stored value

def thing=(thingie) # set
 do something to thingie # compute value OR
 @thing = thingie

attr_writer and attr_accessor both create an instance variable of the form @thing if not defined but which is obviously(!) only valid after it has been set. The form attr :thing, true is equivalent to attr_accessor :thing

alias Core API
# either use as section separator (no parameter)
alias alias_name current_name
# must come AFTER the current_name method
and object condition 1 AND condition 2 alias && (but which has higher precedence than 'and')
array Core API Arrays automatically get Enumerable methods as Mixins. Arrays may be initialized any of the followng means:
ar = # empty array
ar = [] # empty array

# optional size, default value arguments
# default value is returned for any element which 
# has not been assigned
ar =, "a") # ["a", "a"]
ar = # [nil, nil]

# initialising with values
ar = ["a", "a"] 
ar = Array.[]("a", "a")
ar = Array["a", "a"]

# mixed values
ar = [1, "a", 2, 3]
ar << 1 # => [1, "a", 2, 3, 1]
assignment Core API Assignment is an expression
# multiple assignment - same value
a = b = 1

# multiple assigment - multiple values
a,b,c = "one", "two", "three"

# using C style conditional expression to set value
msg = ok.empty? ? "yes" ; "no"

# condition result to set value
msg = if ok.empty? then "yes" else "no" end
attributes Core API Ruby provides support for automatically handling attributes using accessors.
begin Core API Lowercase. The 'begin-end' statements enclose an exception handling block. 'def' has implicit 'begin-end'.
# buggy code!
rescue SomeError
  some code

# def has implicit begin-end so this works
def method
  buggy code!
  rescue SomeError
    some code
NOTE: the keyword BEGIN (uppercase) starts a code block executed first
BEGIN Core API Uppercase. Optional code block enclosed in braces that is executed when the program is loaded/started. May have a corresponding END block which is executed last.
BEGIN {code block}
NOTE: the keyword begin (lowercase) starts an exception sequence
block_given? Kernel All method calls will accept an optional block - block_given? allows its presence to be tested either to conditionally generate a result or to avoid an exception:
# method generates one of two results depending 
# on presence or absence of block
 def somemethod(p1,p2)
  if block_given?  
   p1 + p2

# call with only arguments
somemethod(2,3) # => 5

# call with block
somemethod(2,3) {|x,y| x*x + y*y} # => 13
class object The class statement defines the beginning of a class, terminated with a normal end statement. Most classes have a constructor method (initialize) but this is not a requiremement. Methods within the class may be instance methods or class methods. A class may be used to extend an existing class. Class names are constants and therefore must start with a Capital letter. mixins can be used to extend class methods:
# simple class definition
class Thing

# class extends (includes all methods of) Another class
class Thing < Another
chr object converts a number to a string e.g. 111.chr = "o". Example:
# test for single char in string
if string[0].chr == "a" then do something end
# OR functionally identical
if string[0] == "a"[0] then do something end
closed? Class IO returns true if a file is closed (false if not) UNLESS the file was automatically closed by an iterator function in which case the file reference no longer exists and ruby/mod_ruby will throw an exception.
comparisons object
and   (synonym &&) 
or    (synonym ||)
not   (synonym !)
==    Test for equal value. 
===   Used to test equality within a when clause of 
      a case statement. 
<=>   General comparison operator.
      Returns -1, 0, or +1, depending on whether 
      its receiver is less than, equal to, or
      greater than its argument. 
<, <=, >=, >  Comparison operators for less than,
      less than or equal, greater than or equal, 
      and greater than. 
=~    Regular expression pattern match. 
eql?  True if the receiver and argument have both the
      same type and equal values. 1 == 1.0 returns true,
      but 1.eql?(1.0) is false. 
equal? True if the receiver and argument have the same 
       object id
collect Array, Hash, Set Map is an alias. Returns an array by iterating each element via the code block. Added via enumerable module. Example:
# newarray == other array with 1 added to each element
newarray = old array.collect {|a| a+1}
def Core API Defines the beginning of a method (or function if you prefer). Methods can belong to an instance or the class and can be empty (no arguments are passed) or can take one or more arguments. The method definition is terminated by end:
# definition of a empty instance method
class Thing
 def my_method
# instance method with arguments
class Thing
 def another_method arg1, arg2
# or def another_method (arg1, arg2)

# instance method use
a =
a.another_method(p1,p2) # => some result

# defining a class method
class Thing
 def self.class_method(arg1,arg2)

# usage of class method
Thing.class_method(p1,p2) # => some result

Parameters to def can take multiple forms:
# empty arguments
 def somemethod
# variable name arguments
 def somemethod(p1,p2)
# method call 
# or by using an * in the call arguments can be 
# exploded from an array
# the following is functionally identical to above
 somemethod (*[1,2])
# variable name arguments with defaults
# any or all arguments may have defaults
# evaluated left to right and may reference preceding 
# argument values
 def somemethod(p1,p2=1,p3=p1+1)

# array arguments collection
# adding * to argument name collects into an array 
# which must be last or only argument
# NOTE: any argument can also be an array, this form just uses
#       implicit collection of arguments into an array at the
#       time of the method call
 def somemethod(p1,*p2)

# adds all excess arguments to p2 array above
# 2 and 3 below are placed in array
somemethod (1,2,3) # p1 = 1, p2 = [2,3]

# hash collection of arguments
# used as a type of keyword argument
 def somemethod(p1,p2)

# hash collector shortform for p2 above
# does not need normal brace syntax
somemethod (1,"one" => 1, "two" =>2)

# but could also be written as 
somemethod (1,{"one" => 1, "two" =>2})

# code block argument
# adding & before argument indicates code block
# all methods can be called with an optional code block 
# (see here)
# this syntax causes a Proc class object to be created
# automatically giving access to all Proc methods

# example generates one of three results depending 
# on presence or absence of block and no. of block arguments
 def somemethod(p1,p2,&p3)
  if block_given?  
   if p3.arity == 1 # .arity returns count 
                    # of arguments in block
   p1 + p2

# call with only arguments
somemethod(2,3) # => 5
# call with block and two arguments
somemethod(2,3) {|x,y| x*x + y*y} # => 13
# call with block and one argument
somemethod(2,3) {|x| x*x} # => 4
defined? object returns nil if 'thing' does not exist (has not been defined). Used to check for presence of method, expression, variable etc. This NOT a method and hence does not return a boolean. Sigh.
defined? thing # => nil does not exist
# if it does exist, may return one of:
# expression, super, assignment, method, 
# yield, self, nil, true, false, assignment,
# local-variable, local-variable(in-block)
# global-variable, instance-variable, constant,
# class variable

Glossary Navigation

Select from the range below:

Symbols ?, #, ::, etc. | a - d | e - l | m - r | s - z

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