ruby - strings, symbols, and other scalar objects

Ruby - String, Symbol and other scalar objects

@farhan_faruque

What?

❖ Strings - handling text material of any length❖ Symbol - another way of representing text

String notation “This is a string” ‘This is also a string’

➔ single vs double-quoted string interpolation doesn’t work with single-quoted strings

puts "Two plus two is #{2 + 2}." => Two plus two is 4puts 'Two plus two is #{2 + 2}.' => Two plus two is #{2 + 2}.

Escape interpolation➔ Backslash(\) uses for escape the string interpolation mechanism in

a double-quoted string puts "Escaped interpolation: \"\#{2 + 2}\"."

=> Two plus two is #{2 + 2}.

QUOTING MECHANISMS

➔ % char {text}◆ %q produces a single-quoted string

puts %q{You needn't escape apostrophes when using %q.}

◆ %Q produces a double-quoted string

Basic String manipulation➔ retrieve the nth character in a string, use the [] operator/method

>> string = "Ruby is a cool language."=> "Ruby is a cool language.">> string[5]=> “i”>> string[-12]

=> “o”

➔ substring>> string[5,10]=> "is a cool "

Basic String manipulation..➔ Explicit substring search

>> string["cool lang"]=> "cool lang">> string["very cool lang"]=> nil

➔ slice!- remove the character(s) from the string permanently

>> string.slice!("cool ")=>"cool ">> string=>"Ruby is a language."

Basic String manipulation..➔ [] = method

- It takes the same kinds of indexing arguments as [] but changes the values to what you specify>> string["cool"] = "great"=> “great”>> string=> "Ruby is a great language."

Integers, ranges, strings, and regular expressions can thus all work as index or substring specifiers.

COMBINING STRINGS➔ use the + method

>> "a" + "b" + "c"

=> “abc”

➔ To add (append) a second string permanently, use the << method>> str = "Hi " => "Hi”>> str <<"there." => “Hi there”>> str => “Hi there”

COMBINATION VIA INTERPOLATION

>> str = "Hi " => "Hi " >> "#{str} there." => "Hi there."

➔ The code inside the curly braces can be anything.

Querying strings➔ BOOLEAN STRING QUERIES

include? - start_with? - end_with? - empty?>> string.include?("Ruby") => true>> string.start_with?("Ruby") => true

➔ CONTENT QUERIESsize length>> string.size=> 24

Querying stringscount method

- use for many times a given letter or set of letters occurs in a string>> string.count("a") => 3

- To count how many of a range of letters there are, you can use a hyphen-separated range>> string.count("g-m") => 5

- To negate the search,to count the number of characters that don’t match >> string.count("^aey. ") => 14

String comparison and ordering

➔ The String class mixes in the Comparable module and defines a <=> method>> "a" <=> "b" => -1the spaceship method/operator returns -1 if the right object is greater, 1 if the left object is greater, and 0 if the two objects are equal

➔ COMPARING TWO STRINGS FOR EQUALITY- string comparison method is ==

>> "string" == "string"=> true

String comparison and ordering➔ Another equality-test method, String#eql? same as ==

- String#equal? it tests whether two strings are the same object.>> "a".equal?("a")=> false

String transformation➔ CASE TRANSFORMATIONS >> string = "David A. Black" => "David A. Black" >> string.upcase => "DAVID A. BLACK" >> string.downcase => ”david a. black" >> string.swapcase => "dAVID a. bLACK" >> string.capitalize => "David A. Black"

String transformation➔ FORMATTING TRANSFORMATIONS

- The rjust and ljust methods expand the size of your string to the length provide in the first argument

>> string = "David A. Black" => "David A. Black"

>> string.rjust(25) => " David A. Black"

>> string.ljust(25) => "David A. Black "

>> string.rjust(25,'.') => "...........David A. Black"

String transformation➔ Stripping whitespace from either or both sides,using the strip ,

lstrip , and rstrip methods >> string = " David A. Black" => David A. Black " >> string.strip => "David A. Black" >> string.lstrip => "David A. Black " >> string.rstrip => " David A. Black"

String transformation➔ CONTENT TRANSFORMATIONS

- chop removes a character unconditionally- chomp removes a target substring if it finds that substring at the end of the

string>> "David A. Black".chop => "David A. Blac">> "David A. Black\n".chomp => "David A. Black">> "David A. Black".chomp(ck) => "David A. Bla"

- clear method, which empties a string of all its characters- replace , replaces the current content of the string

clear,replace method permanently changes the string.

String conversionsThe to_i method is one of the conversion methods available to strings.>> "100".to_i(17) => 289 #Interpret "100" as a base 17 number

Other conversion methods available to strings include - to_f (to float)-- to_s (to string;it returns its receiver) - to_sym or intern, which converts the string to a Symbol object. >> "1.2345and some words".to_f=> 1.2345

String encoding➔ SETTING THE ENCODING OF THE SOURCE FILE

- By default, Ruby source files use the US-ASCII encoding.- To change the encoding of a source file, we need to use a magic comment at

the top of the file. The magic comment takes the form# coding: encoding

Example:# coding: UTF-8puts "Euros are designated with this symbol: €"

=> Euros are designated with this symbol: €

String encoding➔ ENCODING OF INDIVIDUAL STRINGS

- we can encode a string with a different encoding, as long as the conversion from the original encoding to the new one—the transcoding—is permitted .

>> str.encode("UTF-8")=> "Test string

Symbols and their usesSymbols?

- instances of the built-in Ruby class Symbol- have a literal constructor: the leading colon

Example::a:book:”this is a symbol”

to_sym - create a symbol programmatically by calling the to_sym method

>> "a".to_sym=> :a

Characteristics of symbols➔ IMMUTABILITY

- Like an integer, a symbol can’t be changed.➔ UNIQUENESS

- Symbols are unique- symbols are more like integers than strings in this respect

>> "abc".object_id => 2707250>> "abc".object_id => 2704780>> :abc.object_id => 160488>> :abc.object_id => 160488

Ruby has no Symbol#new method

Symbols and identifiersSymbol.all_symbols

- returns list of all symbols- a table of symbol

Symbol added when - assign a value to a variable or constant- create a class- write a method

>> Symbol.all_symbols.size => 2025>> a = 1 =>1>> Symbol.all_symbols.size >> 2026>> Symbol.all_symbols.include?(:a) =>true

Symbols and identifiers➔ any symbol Ruby sees anywhere in the program is added>> a = :x => :x>> Symbol.all_symbols.size => 2027>> Symbol.all_symbols.include?(:x) =>true

Symbols in practice➔ SYMBOLS AS METHOD ARGUMENTS

attr_accessor :nameattr_reader :age

➔ SYMBOLS AS HASH KEYS>> d_hash = { :name => "David", :age => 49 } =>{:name=>"David", :age=>49}>>d_hash[:age] => 49

● symbols are more like integers then like strings● a variable to which a symbol is bound provides the actual symbol value, not

a reference to it

Numerical objects➔ numbers are objects

n = 99.6m = n.roundputs m

➔ Numerical classesNumeric

Float Integer

Fixnum Bignum

Times and datesrequire 'date', require 'time' package Times and dates are manipulated through three classes: Time , Date , and DateTime

● 'date' package the Date and DateTime classes● 'time' package enhances the Time class

Instantiating date/time objects➔ CREATING DATE OBJECTS

- Date.today constructor>> Date.today=> #<Date: 4909565/2,0,2299161>

- Date.new >> puts Date.new(1959,2,1)=> 1959-02-01

- parse constructor>> puts Date.parse("03/6/9")=> 2003-06-09

Instantiating date/time objects➔ CREATING TIME OBJECTSwe can create a time object using any of several constructors: new (a.k.a. now), at, local (a.k.a. mktime), and parse.>> Time.new=> 2008-12-03 12:16:21 +0000>> Time.at(100000000)=> 1973-03-03 09:46:40 +0000>> Time.mktime(2007,10,3,14,3,6)=> 2007-10-03 14:03:06 +0100

Instantiating date/time objects➔ CREATING DATETIME OBJECTS

>> puts DateTime.new(2009, 1, 2, 3, 4, 5)2009-01-02T03:04:05+00:00=> nil>> puts DateTime.now2008-12-04T09:09:28+00:00=> nil>> puts DateTime.parse("October 23, 1973, 10:34 AM")1973-10-23T10:34:00+00:00

Date/time query methodsTime objects can be queried as to their year, month, day, hour, minute, andsecond, as can datetime objects. Date objects can be queried as to their year, month, and day:>> dt = DateTime.now=> #<DateTime: 2008-12-04T09:11:32+00:00 26511892736584919/10800000000,0/1,2299161)>>> dt.year => 2008>> dt.hour => 9we can determine whether the given time/date is or isn’t a particular day of the week >> d.monday? => false

Date/time formatting methodsAll date/time objects have the strftime method, which allows to format their fields in a flexible way using format strings, in the style of the strftime(3) system library:>> t = Time.now=> 2008-12-04 09:22:09 +0000>>t.strftime("%m-%d-%Y")=> "12-04-2008"

Common time and date format specifiersSpecifier Description%Y Year (four digits)

%m Month (number)

%d Day of month (left-padded with zeros)

%a , %A Short day name, full day name

%H , %I Hour (24-hour clock), hour (12-hour clock)

%M Minute

%S Second

%x Equivalent to "%m/%d/%y"

Date/time conversion methodsTime has to_date and to_datetime methodsDate has to_time and to_datetime DateTime has to_time and to_date .DATE/TIME ARITHMETIC Time objects let you add and subtract seconds from them, returning a new time object>> t = Time.now=> 2008-12-04 09:33:43 +0000>> t - 20=> 2008-12-04 09:33:23 +0000

DATE/TIME ARITHMETICDate and datetime objects interpret + and – as day-wise operations, and they allow for month-wise conversions with << and >>>> dt = DateTime.now=> #<DateTime: 2015-03-25T22:00:10+06:00...>>> puts dt + 100=> 2015-07-03T22:00:10+06:00>> puts dt >> 3=> 2015-06-25T22:00:10+06:00>> puts dt << 10=> 2014-05-25T22:00:10+06:00

DATE/TIME ARITHMETICMove ahead one using the next (a.k.a. succ ) method.A whole family of next_unit and prev_unit methods move back and forth by day(s), month(s), or year(s):

>> d = Date.today => #<Date: 2008-12-04 (4909609/2,0,2299161)>>> puts d.next =>2008-12-05>> puts d.next_year => 2009-12-04>> puts d.next_month(3) =>2009-03-04>> puts d.prev_day(10) =>2008-11-24

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