Category: Methods

Hashes

A Hash is a collection of key-value pairs like this: “employee” = > “salary”. It is similar to an Array, except that indexing is done via arbitrary keys of any object type, not an integer index.

The order in which you traverse a hash by either key or value may seem arbitrary and will generally not be in the insertion order. If you attempt to access a hash with a key that does not exist, the method will return nil.

Creating Hashes

As with arrays, there is a variety of ways to create hashes. You can create an empty hash with the new class method −

months = Hash.new

You can also use new to create a hash with a default value, which is otherwise just nil −

months = Hash.new( "month" )

or

months = Hash.new "month"

When you access any key in a hash that has a default value, if the key or value doesn’t exist, accessing the hash will return the default value −

#!/usr/bin/ruby

months =Hash.new("month")

puts "#{months[0]}"
puts "#{months[72]}"

This will produce the following result −

month
month

#!/usr/bin/rubyH=Hash["a"=>100,"b"=>200]

puts "#{H['a']}"
puts "#{H['b']}"

This will produce the following result −

100
200

You can use any Ruby object as a key or value, even an array, so the following example is a valid one −

[1,"jan"]=>"January"

Hash Built-in Methods

We need to have an instance of Hash object to call a Hash method. As we have seen, following is the way to create an instance of Hash object −

Hash[[key =>|, value]*]orHash.new[or]Hash.new(obj)[or]Hash.new{|hash, key| block }

This will return a new hash populated with the given objects. Now using the created object, we can call any available instance methods. For example −

#!/usr/bin/ruby

$,=", "
months =Hash.new("month")
months ={"1"=>"January","2"=>"February"}

keys = months.keys
puts "#{keys}"

This will produce the following result −

["1", "2"]

Following are the public hash methods (assuming hash is an array object) −

Sr.No.	Methods & Description
1	hash == other_hashTests whether two hashes are equal, based on whether they have the same number of key-value pairs, and whether the key-value pairs match the corresponding pair in each hash.
2	hash.[key]Using a key, references a value from hash. If the key is not found, returns a default value.
3	hash.[key] = valueAssociates the value given by value with the key given by key.
4	hash.clearRemoves all key-value pairs from hash.
5	hash.default(key = nil)Returns the default value for hash, nil if not set by default=. ([] returns a default value if the key does not exist in hash.)
6	hash.default = objSets a default value for hash.
7	hash.default_procReturns a block if hash was created by a block.
8	hash.delete(key) [or]array.delete(key) { \|key\| block }Deletes a key-value pair from hash by key. If block is used, returns the result of a block if pair is not found. Compare delete_if.
9	hash.delete_if { \|key,value\| block }Deletes a key-value pair from hash for every pair the block evaluates to true.
10	hash.each { \|key,value\| block }Iterates over hash, calling the block once for each key, passing the key-value as a two-element array.
11	hash.each_key { \|key\| block }Iterates over hash, calling the block once for each key, passing key as a parameter.
12	hash.each_key { \|key_value_array\| block }Iterates over hash, calling the block once for each key, passing the key and value as parameters.
13	hash.each_key { \|value\| block }Iterates over hash, calling the block once for each key, passing value as a parameter.
14	hash.empty?Tests whether hash is empty (contains no key-value pairs), returning true or false.
15	hash.fetch(key [, default] ) [or]hash.fetch(key) { \| key \| block }Returns a value from hash for the given key. If the key can’t be found, and there are no other arguments, it raises an IndexError exception; if default is given, it is returned; if the optional block is specified, its result is returned.
16	hash.has_key?(key) [or] hash.include?(key) [or]hash.key?(key) [or] hash.member?(key)Tests whether a given key is present in hash, returning true or false.
17	hash.has_value?(value)Tests whether hash contains the given value.
18	hash.index(value)Returns the key for the given value in hash, nil if no matching value is found.
19	hash.indexes(keys)Returns a new array consisting of values for the given key(s). Will insert the default value for keys that are not found. This method is deprecated. Use select.
20	hash.indices(keys)Returns a new array consisting of values for the given key(s). Will insert the default value for keys that are not found. This method is deprecated. Use select.
21	hash.inspectReturns a pretty print string version of hash.
22	hash.invertCreates a new hash, inverting keys and values from hash; that is, in the new hash, the keys from hash become values and values become keys.
23	hash.keysCreates a new array with keys from hash.
24	hash.lengthReturns the size or length of hash as an integer.
25	hash.merge(other_hash) [or]hash.merge(other_hash) { \|key, oldval, newval\| block }Returns a new hash containing the contents of hash and other_hash, overwriting pairs in hash with duplicate keys with those from other_hash.
26	hash.merge!(other_hash) [or]hash.merge!(other_hash) { \|key, oldval, newval\| block }Same as merge, but changes are done in place.
27	hash.rehashRebuilds hash based on the current values for each key. If values have changed since they were inserted, this method reindexes hash.
28	hash.reject { \|key, value\| block }Creates a new hash for every pair the block evaluates to true
29	hash.reject! { \|key, value\| block }Same as reject, but changes are made in place.
30	hash.replace(other_hash)Replaces the contents of hash with the contents of other_hash.
31	hash.select { \|key, value\| block }Returns a new array consisting of key-value pairs from hash for which the block returns true.
32	hash.shiftRemoves a key-value pair from hash, returning it as a two-element array.
33	hash.sizeReturns the size or length of hash as an integer.
34	hash.sortConverts hash to a two-dimensional array containing arrays of key-value pairs, then sorts it as an array.
35	hash.store(key, value)Stores a key-value pair in hash.
36	hash.to_aCreates a two-dimensional array from hash. Each key/value pair is converted to an array, and all these arrays are stored in a containing array.
37	hash.to_hashReturns hash (self).
38	hash.to_sConverts hash to an array, then converts that array to a string.
39	hash.update(other_hash) [or]hash.update(other_hash) {\|key, oldval, newval\| block}Returns a new hash containing the contents of hash and other_hash, overwriting pairs in hash with duplicate keys with those from other_hash.
40	hash.value?(value)Tests whether hash contains the given value.
41	hash.valuesReturns a new array containing all the values of hash.
42	hash.values_at(obj, …)Returns a new array containing the values from hash that are associated with the given key or keys.

August 19, 2025

Arrays
Ruby arrays are ordered, integer-indexed collections of any object. Each element in an array is associated with and referred to by an index.

Array indexing starts at 0, as in C or Java. A negative index is assumed relative to the end of the array — that is, an index of -1 indicates the last element of the array, -2 is the next to last element in the array, and so on.

Ruby arrays can hold objects such as String, Integer, Fixnum, Hash, Symbol, even other Array objects. Ruby arrays are not as rigid as arrays in other languages. Ruby arrays grow automatically while adding elements to them.

Creating Arrays

There are many ways to create or initialize an array. One way is with the new class method −
```
names =Array.new
```
You can set the size of an array at the time of creating array −
```
names =Array.new(20)
```
The array names now has a size or length of 20 elements. You can return the size of an array with either the size or length methods −
```
#!/usr/bin/ruby

names =Array.new(4,"mac")
puts "#{names}"
```
This will produce the following result −
```
["mac", "mac", "mac", "mac"]
```
You can also use a block with new, populating each element with what the block evaluates to −
```
#!/usr/bin/ruby

nums =Array.new(10){|e| e = e *2}
puts "#{nums}"
```
This will produce the following result −
```
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
```
There is another method of Array, []. It works like this −
```
nums =Array.[](1,2,3,4,5)
```
One more form of array creation is as follows −
```
nums =Array[1,2,3,4,5]
```
The Kernel module available in core Ruby has an Array method, which only accepts a single argument. Here, the method takes a range as an argument to create an array of digits −
```
#!/usr/bin/ruby

digits =Array(0..9)
puts "#{digits}"
```
This will produce the following result −
```
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
```
Array Built-in Methods

We need to have an instance of Array object to call an Array method. As we have seen, following is the way to create an instance of Array object −
```
Array.[](...) [or] Array[...] [or] [...]
```
This will return a new array populated with the given objects. Now, using the created object, we can call any available instance methods. For example −
```
#!/usr/bin/ruby

digits =Array(0..9)
num = digits.at(6)
puts "#{num}"
```
This will produce the following result −
```
6
```
Following are the public array methods (assuming array is an array object) −

Array pack Directives

Following table lists the pack directives for use with Array#pack.

Example

Try the following example to pack various data.
```
a =["a","b","c"]
n =[65,66,67]
puts a.pack("A3A3A3")#=> "a  b  c  "
puts a.pack("a3a3a3")#=> "a\000\000b\000\000c\000\000"
puts n.pack("ccc")#=> "ABC"
```
This will produce the following result −
```
a  b  c
abc
ABC
```
August 19, 2025
Strings
A String object in Ruby holds and manipulates an arbitrary sequence of one or more bytes, typically representing characters that represent human language.

The simplest string literals are enclosed in single quotes (the apostrophe character). The text within the quote marks is the value of the string −
```
'This is a simple Ruby string literal'
```
If you need to place an apostrophe within a single-quoted string literal, precede it with a backslash, so that the Ruby interpreter does not think that it terminates the string −
```
'Won\'t you read O\'Reilly\'s book?'
```
The backslash also works to escape another backslash, so that the second backslash is not itself interpreted as an escape character.

Following are the string-related features of Ruby.

Expression Substitution

Expression substitution is a means of embedding the value of any Ruby expression into a string using #{ and } −
```
#!/usr/bin/ruby

x, y, z =12,36,72
puts "The value of x is #{ x }."
puts "The sum of x and y is #{ x + y }."
puts "The average was #{ (x + y + z)/3 }."
```
This will produce the following result −
```
The value of x is 12.
The sum of x and y is 48.
The average was 40.
```
General Delimited Strings

With general delimited strings, you can create strings inside a pair of matching though arbitrary delimiter characters, e.g., !, (, {, <, etc., preceded by a percent character (%). Q, q, and x have special meanings. General delimited strings can be −
```
%{Ruby is fun.}  equivalent to "Ruby is fun."
%Q{ Ruby is fun. } equivalent to " Ruby is fun. "
%q[Ruby is fun.]  equivalent to a single-quoted string
%x!ls! equivalent to back tick command output ls
```
Escape Characters

Following table is a list of escape or non-printable characters that can be represented with the backslash notation.

Character Encoding

The default character set for Ruby is ASCII, whose characters may be represented by single bytes. If you use UTF-8, or another modern character set, characters may be represented in one to four bytes.

You can change your character set using $KCODE at the beginning of your program, like this −
```
$KCODE = 'u'
```
Following are the possible values for $KCODE.

String Built-in Methods

We need to have an instance of String object to call a String method. Following is the way to create an instance of String object −
```
new [String.new(str = "")]
```
This will return a new string object containing a copy of str. Now, using str object, we can all use any available instance methods. For example −
```
#!/usr/bin/ruby

myStr =String.new("THIS IS TEST")
foo = myStr.downcase

puts "#{foo}"
```
This will produce the following result −
```
this is test
```
Following are the public String methods ( Assuming str is a String object ) −

String unpack Directives

Following table lists the unpack directives for method String#unpack.

Example

Try the following example to unpack various data.
```
"abc \0\0abc \0\0".unpack('A6Z6')#=> ["abc", "abc "]"abc \0\0".unpack('a3a3')#=> ["abc", " \000\000"]"abc \0abc \0".unpack('Z*Z*')#=> ["abc ", "abc "]"aa".unpack('b8B8')#=> ["10000110", "01100001"]"aaa".unpack('h2H2c')#=> ["16", "61", 97]"\xfe\xff\xfe\xff".unpack('sS')#=> [-2, 65534]"now = 20is".unpack('M*')#=> ["now is"]"whole".unpack('xax2aX2aX1aX2a')#=> ["h", "e", "l", "l", "o"]
```
August 19, 2025
Modules and Mixins
Modules are a way of grouping together methods, classes, and constants. Modules give you two major benefits.
- Modules provide a namespace and prevent name clashes.
- Modules implement the mixin facility.
Modules define a namespace, a sandbox in which your methods and constants can play without having to worry about being stepped on by other methods and constants.

Syntax
```
module Identifier
   statement1
   statement2
   ...........
end
```
Module constants are named just like class constants, with an initial uppercase letter. The method definitions look similar, too: Module methods are defined just like class methods.

As with class methods, you call a module method by preceding its name with the module’s name and a period, and you reference a constant using the module name and two colons.

Example
```
#!/usr/bin/ruby# Module defined in trig.rb filemoduleTrigPI=3.141592654defTrig.sin(x)# ..enddefTrig.cos(x)# ..endend
```
We can define one more module with the same function name but different functionality −
```
#!/usr/bin/ruby# Module defined in moral.rb filemoduleMoralVERY_BAD=0BAD=1defMoral.sin(badness)# ...endend
```
Like class methods, whenever you define a method in a module, you specify the module name followed by a dot and then the method name.

Ruby require Statement

The require statement is similar to the include statement of C and C++ and the import statement of Java. If a third program wants to use any defined module, it can simply load the module files using the Ruby require statement −

Syntax
```
require filename
```
Here, it is not required to give .rb extension along with a file name.

Example
```
$LOAD_PATH<<'.'require'trig.rb'require'moral'

y =Trig.sin(Trig::PI/4)
wrongdoing =Moral.sin(Moral::VERY_BAD)
```
Here we are using $LOAD_PATH << ‘.’ to make Ruby aware that included files must be searched in the current directory. If you do not want to use $LOAD_PATH then you can use require_relative to include files from a relative directory.

IMPORTANT − Here, both the files contain the same function name. So, this will result in code ambiguity while including in calling program but modules avoid this code ambiguity and we are able to call appropriate function using module name.

Ruby include Statement

You can embed a module in a class. To embed a module in a class, you use the include statement in the class −

Syntax
```
include modulename
```
If a module is defined in a separate file, then it is required to include that file using require statement before embedding module in a class.

Example

Consider the following module written in support.rb file.
```
module Week
   FIRST_DAY = "Sunday"
   def Week.weeks_in_month
  puts "You have four weeks in a month"   end
   def Week.weeks_in_year
  puts "You have 52 weeks in a year"   end
end
```
Now, you can include this module in a class as follows −
```
#!/usr/bin/ruby
$LOAD_PATH << '.'
require "support"

class Decade
include Week
   no_of_yrs = 10
   def no_of_months
  puts Week::FIRST_DAY
  number = 10*12
  puts number   end
end
d1 = Decade.new
puts Week::FIRST_DAY
Week.weeks_in_month
Week.weeks_in_year
d1.no_of_months
```
This will produce the following result −
```
Sunday
You have four weeks in a month
You have 52 weeks in a year
Sunday
120
```
Mixins in Ruby

Before going through this section, we assume you have the knowledge of Object Oriented Concepts.

When a class can inherit features from more than one parent class, the class is supposed to show multiple inheritance.

Ruby does not support multiple inheritance directly but Ruby Modules have another wonderful use. At a stroke, they pretty much eliminate the need for multiple inheritance, providing a facility called a mixin.

Mixins give you a wonderfully controlled way of adding functionality to classes. However, their true power comes out when the code in the mixin starts to interact with code in the class that uses it.

Let us examine the following sample code to gain an understand of mixin −
```
moduleAdefa1enddefa2endendmoduleBdefb1enddefb2endendclassSampleincludeAincludeBdefs1endend

samp =Sample.new
samp.a1
samp.a2
samp.b1
samp.b2
samp.s1
```
Module A consists of the methods a1 and a2. Module B consists of the methods b1 and b2. The class Sample includes both modules A and B. The class Sample can access all four methods, namely, a1, a2, b1, and b2. Therefore, you can see that the class Sample inherits from both the modules. Thus, you can say the class Sample shows multiple inheritance or a mixin.
August 19, 2025
Blocks
You have seen how Ruby defines methods where you can put number of statements and then you call that method. Similarly, Ruby has a concept of Block.
- A block consists of chunks of code.
- You assign a name to a block.
- The code in the block is always enclosed within braces ({}).
- A block is always invoked from a function with the same name as that of the block. This means that if you have a block with the name test, then you use the function test to invoke this block.
- You invoke a block by using the yield statement.
Syntax
```
block_name {
   statement1
   statement2
   ..........
}
```
Here, you will learn to invoke a block by using a simple yield statement. You will also learn to use a yield statement with parameters for invoking a block. You will check the sample code with both types of yield statements.

The yield Statement

Let’s look at an example of the yield statement −
```
#!/usr/bin/rubydeftest
   puts "You are in the method"yield
   puts "You are again back to the method"yieldend
test {puts "You are in the block"}
```
This will produce the following result −
```
You are in the method
You are in the block
You are again back to the method
You are in the block
```
You also can pass parameters with the yield statement. Here is an example −
```
#!/usr/bin/rubydeftestyield5
   puts "You are in the method test"yield100end
test {|i| puts "You are in the block #{i}"}
```
This will produce the following result −
```
You are in the block 5
You are in the method test
You are in the block 100
```
Here, the yield statement is written followed by parameters. You can even pass more than one parameter. In the block, you place a variable between two vertical lines (||) to accept the parameters. Therefore, in the preceding code, the yield 5 statement passes the value 5 as a parameter to the test block.

Now, look at the following statement −
```
test {|i| puts "You are in the block #{i}"}
```
Here, the value 5 is received in the variable i. Now, observe the following puts statement −
```
puts "You are in the block #{i}"
```
The output of this puts statement is −
```
You are in the block 5
```
If you want to pass more than one parameters, then the yield statement becomes −
```
yield a, b
```
and the block is −
```
test {|a, b| statement}
```
The parameters will be separated by commas.

Blocks and Methods

You have seen how a block and a method can be associated with each other. You normally invoke a block by using the yield statement from a method that has the same name as that of the block. Therefore, you write −
```
#!/usr/bin/rubydeftestyieldend
test{ puts "Hello world"}
```
This example is the simplest way to implement a block. You call the test block by using the yield statement.

But if the last argument of a method is preceded by &, then you can pass a block to this method and this block will be assigned to the last parameter. In case both * and & are present in the argument list, & should come later.
```
#!/usr/bin/rubydeftest(&block)
   block.call
end
test { puts "Hello World!"}
```
This will produce the following result −
```
Hello World!
```
BEGIN and END Blocks

Every Ruby source file can declare blocks of code to be run as the file is being loaded (the BEGIN blocks) and after the program has finished executing (the END blocks).
```
#!/usr/bin/rubyBEGIN{# BEGIN block code 
   puts "BEGIN code block"}END{# END block code 
   puts "END code block"}# MAIN block code 
puts "MAIN code block"
```
A program may include multiple BEGIN and END blocks. BEGIN blocks are executed in the order they are encountered. END blocks are executed in reverse order. When executed, the above program produces the following result −
```
BEGIN code block
MAIN code block
END code block
```
August 19, 2025
Methods
Ruby methods are very similar to functions in any other programming language. Ruby methods are used to bundle one or more repeatable statements into a single unit.

Method names should begin with a lowercase letter. If you begin a method name with an uppercase letter, Ruby might think that it is a constant and hence can parse the call incorrectly.

Methods should be defined before calling them, otherwise Ruby will raise an exception for undefined method invoking.

Syntax
```
def method_name [( [arg [= default]]...[, * arg [, &expr ]])]
   expr..
end
```
So, you can define a simple method as follows −
```
def method_name 
   expr..
end
```
You can represent a method that accepts parameters like this −
```
def method_name (var1, var2)
   expr..
end
```
You can set default values for the parameters, which will be used if method is called without passing the required parameters −
```
def method_name (var1 = value1, var2 = value2)
   expr..
end
```
Whenever you call the simple method, you write only the method name as follows −
```
method_name
```
However, when you call a method with parameters, you write the method name along with the parameters, such as −
```
method_name 25, 30
```
The most important drawback to using methods with parameters is that you need to remember the number of parameters whenever you call such methods. For example, if a method accepts three parameters and you pass only two, then Ruby displays an error.

Example
```
#!/usr/bin/rubydeftest(a1 ="Ruby", a2 ="Perl")
   puts "The programming language is #{a1}"
   puts "The programming language is #{a2}"end
test "C","C++"
test
```
This will produce the following result −
```
The programming language is C
The programming language is C++
The programming language is Ruby
The programming language is Perl
```
Return Values from Methods

Every method in Ruby returns a value by default. This returned value will be the value of the last statement. For example −
```
deftest
   i =100
   j =10
   k =0end
```
This method, when called, will return the last declared variable k.

Ruby return Statement

The return statement in ruby is used to return one or more values from a Ruby Method.

Syntax
```
return [expr[`,' expr...]]
```
If more than two expressions are given, the array containing these values will be the return value. If no expression given, nil will be the return value.

Example
```
returnORreturn12ORreturn1,2,3
```
Have a look at this example −
```
#!/usr/bin/rubydeftest
   i =100
   j =200
   k =300return i, j, k
end
var = test
puts var
```
This will produce the following result −
```
100
200
300
```
Variable Number of Parameters

Suppose you declare a method that takes two parameters, whenever you call this method, you need to pass two parameters along with it.

However, Ruby allows you to declare methods that work with a variable number of parameters. Let us examine a sample of this −
```
#!/usr/bin/rubydefsample(*test)
   puts "The number of parameters is #{test.length}"for i in0...test.length
  puts "The parameters are #{test[i]}"endendsample "Zara","6","F"
sample "Mac","36","M","MCA"
```
In this code, you have declared a method sample that accepts one parameter test. However, this parameter is a variable parameter. This means that this parameter can take in any number of variables. So, the above code will produce the following result −
```
The number of parameters is 3
The parameters are Zara
The parameters are 6
The parameters are F
The number of parameters is 4
The parameters are Mac
The parameters are 36
The parameters are M
The parameters are MCA
```
Class Methods

When a method is defined outside of the class definition, the method is marked as private by default. On the other hand, the methods defined in the class definition are marked as public by default. The default visibility and the private mark of the methods can be changed by public or private of the Module.

Whenever you want to access a method of a class, you first need to instantiate the class. Then, using the object, you can access any member of the class.

Ruby gives you a way to access a method without instantiating a class. Let us see how a class method is declared and accessed −
```
classAccountsdefreading_chargeenddefAccounts.return_dateendend
```
See how the method return_date is declared. It is declared with the class name followed by a period, which is followed by the name of the method. You can access this class method directly as follows −
```
Accounts.return_date
```
To access this method, you need not create objects of the class Accounts.

Ruby alias Statement

This gives alias to methods or global variables. Aliases cannot be defined within the method body. The alias of the method keeps the current definition of the method, even when methods are overridden.

Making aliases for the numbered global variables (&dollar;1, &dollar;2,…) is prohibited. Overriding the built-in global variables may cause serious problems.

Syntax
```
alias method-name method-name
alias global-variable-name global-variable-name
```
Example
```
alias foo bar
alias &dollar;MATCH &dollar;&
```
Here we have defined foo alias for bar, and &dollar;MATCH is an alias for &dollar;&

Ruby undef Statement

This cancels the method definition. An undef cannot appear in the method body.

By using undef and alias, the interface of the class can be modified independently from the superclass, but notice it may be broke programs by the internal method call to self.

Syntax
```
undef method-name
```
Example

To undefine a method called bar do the following −
```
undef bar
```
August 19, 2025

Category: Methods

Hashes

Creating Hashes

Hash Built-in Methods

Arrays

Creating Arrays

Array Built-in Methods

Array pack Directives

Example

Strings

Expression Substitution

General Delimited Strings

Escape Characters

Character Encoding

String Built-in Methods

String unpack Directives

Example

Modules and Mixins

Syntax

Example

Ruby require Statement

Syntax

Example

Ruby include Statement

Syntax

Example

Mixins in Ruby

Blocks

Syntax

The yield Statement

Blocks and Methods

BEGIN and END Blocks

Methods

Syntax

Example

Return Values from Methods

Ruby return Statement

Syntax

Example

Variable Number of Parameters

Class Methods

Ruby alias Statement

Syntax

Example

Ruby undef Statement

Syntax

Example