U:RDoc::TopLevel[ iI"syntax/methods.rdoc:EFcRDoc::Parser::Simpleo:RDoc::Markup::Document: @parts[S:RDoc::Markup::Heading: leveli: textI" Methods;To:RDoc::Markup::BlankLineo:RDoc::Markup::Paragraph;[I"SMethods implement the functionality of your program. Here is a simple method ;TI"definition:;T@ o:RDoc::Markup::Verbatim;[I"def one_plus_one ;TI" 1 + 1 ;TI" end ;T: @format0o; ;[I"SA method definition consists of the +def+ keyword, a method name, the body of ;TI"Tthe method, +return+ value and the +end+ keyword. When called the method will ;TI">execute the body of the method. This method returns +2+.;T@ o; ;[I"TThis section only covers defining methods. See also the {syntax documentation ;TI"?on calling methods}[rdoc-ref:syntax/calling_methods.rdoc].;T@ S; ; i; I"Method Names;T@ o; ;[ I"TMethod names may be one of the operators or must start a letter or a character ;TI"Pwith the eight bit set. It may contain letters, numbers, an _ ;TI"T(underscore or low line) or a character with the eight bit set. The convention ;TI"His to use underscores to separate words in a multiword method name:;T@ o;;[I"def method_name ;TI"0 puts "use underscores to separate words" ;TI" end ;T;0o; ;[ I"RRuby programs must be written in a US-ASCII-compatible character set such as ;TI"NUTF-8, ISO-8859-1 etc. In such character sets if the eight bit is set it ;TI"Uindicates an extended character. Ruby allows method names and other identifiers ;TI"Sto contain such characters. Ruby programs cannot contain some characters like ;TI"#ASCII NUL (\x00).;T@ o; ;[I":The following are the examples of valid ruby methods:;T@ o;;[ I"def hello ;TI" "hello" ;TI" end ;TI" ;TI"def こんにちは ;TI"& puts "means hello in Japanese" ;TI" end ;T;0o; ;[I"PTypically method names are US-ASCII compatible since the keys to type them ;TI"exist on all keyboards.;T@ o; ;[I"NMethod names may end with a ! (bang or exclamation mark), a ;TI"B? (question mark) or = equals sign.;T@ o; ;[I"PThe bang methods (! at the end of method name) are called and ;TI"Sexecuted just like any other method. However, by convention, a method with an ;TI"Qexclamation point or bang is considered dangerous. In ruby core library the ;TI"Tdangerous method implies that when a method ends with a bang (!), ;TI"Pit indicates that unlike its non-bang equivalent, permanently modifies its ;TI"Ereceiver. Almost always, ruby core library will have a non-bang ;TI"Tcounterpart (method name which does NOT end with !) of every bang ;TI"Rmethod (method name which does end with !) that does not modify ;TI"Othe receiver. This convention is typically true for ruby core library but ;TI"7may or may not hold true for other ruby libraries.;T@ o; ;[I"RMethods that end with a question mark by convention return boolean, but they ;TI"Omay not always return just +true+ or +false+. Often, they will return an ;TI"9object to indicate a true value (or "truthy" value).;T@ o; ;[I"NMethods that end with an equals sign indicate an assignment method. For ;TI"Tassignment methods, the return value is ignored and the arguments are returned ;TI" instead.;T@ o; ;[ I"KThese are method names for the various ruby operators. Each of these ;TI"Poperators accept only one argument. Following the operator is the typical ;TI"Ruse or name of the operator. Creating an alternate meaning for the operator ;TI"Lmay lead to confusion as the user expects plus to add things, minus to ;TI"Qsubtract things, etc. Additionally, you cannot alter the precedence of the ;TI"operators.;T@ o:RDoc::Markup::List: @type: NOTE: @items[o:RDoc::Markup::ListItem: @label[I"+ ;T;[o; ;[I"add;To;;[I"- ;T;[o; ;[I" subtract;To;;[I"* ;T;[o; ;[I" multiply;To;;[I"** ;T;[o; ;[I" power;To;;[I"/ ;T;[o; ;[I" divide;To;;[I"% ;T;[o; ;[I"modulus division, String#%;To;;[I"& ;T;[o; ;[I"AND;To;;[I"^ ;T;[o; ;[I"XOR (exclusive OR);To;;[I">> ;T;[o; ;[I"right-shift;To;;[I"<< ;T;[o; ;[I"left-shift, append;To;;[I"== ;T;[o; ;[I" equal;To;;[I"!= ;T;[o; ;[I"not equal;To;;[I"=== ;T;[o; ;[I"#case equality. See Object#===;To;;[I"=~ ;T;[o; ;[I"7pattern match. (Not just for regular expressions);To;;[I"!~ ;T;[o; ;[I"does not match;To;;[I"<=> ;T;[o; ;[I"7comparison aka spaceship operator. See Comparable;To;;[I"< ;T;[o; ;[I"less-than;To;;[I"<= ;T;[o; ;[I"less-than or equal;To;;[I"> ;T;[o; ;[I"greater-than;To;;[I">= ;T;[o; ;[I"greater-than or equal;T@ o; ;[I"TTo define unary methods minus, plus, tilde and not (!) follow the ;TI"Noperator with an @ as in +@ or !@:;T@ o;;[I" class C ;TI" def -@ ;TI") puts "you inverted this object" ;TI" end ;TI" end ;TI" ;TI"obj = C.new ;TI" ;TI".-obj # prints "you inverted this object" ;T;0o; ;[I")Unary methods accept zero arguments.;T@ o; ;[I"PAdditionally, methods for element reference and assignment may be defined: ;TI"R[] and []= respectively. Both can take one or more ;TI"4arguments, and element reference can take none.;T@ o;;[I" class C ;TI" def [](a, b) ;TI" puts a + b ;TI" end ;TI" ;TI" def []=(a, b, c) ;TI" puts a * b + c ;TI" end ;TI" end ;TI" ;TI"obj = C.new ;TI" ;TI" obj[2, 3] # prints "5" ;TI"!obj[2, 3] = 4 # prints "10" ;T;0S; ; i; I"Return Values;T@ o; ;[ I"UBy default, a method returns the last expression that was evaluated in the body ;TI"Tof the method. In the example above, the last (and only) expression evaluated ;TI"Qwas the simple sum 1 + 1. The +return+ keyword can be used to ;TI"4make it explicit that a method returns a value.;T@ o;;[I"def one_plus_one ;TI" return 1 + 1 ;TI" end ;T;0o; ;[I"OIt can also be used to make a method return before the last expression is ;TI"evaluated.;T@ o;;[ I"def two_plus_two ;TI" return 2 + 2 ;TI"3 1 + 1 # this expression is never evaluated ;TI" end ;T;0o; ;[I"ONote that for assignment methods the return value will always be ignored. ;TI",Instead, the argument will be returned:;T@ o;;[ I"def a=(value) ;TI" return 1 + value ;TI" end ;TI" ;TI"p(a = 5) # prints 5 ;T;0S; ; i; I" Scope;T@ o; ;[I",The standard syntax to define a method:;T@ o;;[I"def my_method ;TI" # ... ;TI" end ;T;0o; ;[I"Radds the method to a class. You can define an instance method on a specific ;TI"$class with the +class+ keyword:;T@ o;;[ I" class C ;TI" def my_method ;TI" # ... ;TI" end ;TI" end ;T;0o; ;[I"TA method may be defined on another object. You may define a "class method" (a ;TI"Rmethod that is defined on the class, not an instance of the class) like this:;T@ o;;[ I" class C ;TI" def self.my_method ;TI" # ... ;TI" end ;TI" end ;T;0o; ;[I"THowever, this is simply a special case of a greater syntactical power in Ruby, ;TI"Othe ability to add methods to any object. Classes are objects, so adding ;TI"@class methods is simply adding methods to the Class object.;T@ o; ;[I"?The syntax for adding a method to an object is as follows:;T@ o;;[ I"greeting = "Hello" ;TI" ;TI"def greeting.broaden ;TI" self + ", world!" ;TI" end ;TI" ;TI"0greeting.broaden # returns "Hello, world!" ;T;0o; ;[ I"M+self+ is a keyword referring to the current object under consideration ;TI"Mby the compiler, which might make the use of +self+ in defining a class ;TI"Mmethod above a little clearer. Indeed, the example of adding a +hello+ ;TI"8method to the class +String+ can be rewritten thus:;T@ o;;[I"def String.hello ;TI" "Hello, world!" ;TI" end ;T;0o; ;[I"UA method defined like this is called a "singleton method". +broaden+ will only ;TI"Uexist on the string instance +greeting+. Other strings will not have +broaden+.;T@ S; ; i; I"Overriding;T@ o; ;[ I"TWhen Ruby encounters the +def+ keyword, it doesn't consider it an error if the ;TI"Dmethod already exists: it simply redefines it. This is called ;TI"N_overriding_. Rather like extending core classes, this is a potentially ;TI"Udangerous ability, and should be used sparingly because it can cause unexpected ;TI"6results. For example, consider this irb session:;T@ o;;[I">> "43".to_i ;TI" => 43 ;TI">> class String ;TI">> def to_i ;TI">> 42 ;TI">> end ;TI" >> end ;TI" => nil ;TI">> "43".to_i ;TI" => 42 ;T;0o; ;[I"KThis will effectively sabotage any code which makes use of the method ;TI"<String#to_i to parse numbers from strings.;T@ S; ; i; I"Arguments;T@ o; ;[I"OA method may accept arguments. The argument list follows the method name:;T@ o;;[I"def add_one(value) ;TI" value + 1 ;TI" end ;T;0o; ;[ I"RWhen called, the user of the +add_one+ method must provide an argument. The ;TI"Targument is a local variable in the method body. The method will then add one ;TI"Kto this argument and return the value. If given +1+ this method will ;TI"return +2+.;T@ o; ;[I"7The parentheses around the arguments are optional:;T@ o;;[I"def add_one value ;TI" value + 1 ;TI" end ;T;0o; ;[I"1Multiple arguments are separated by a comma:;T@ o;;[I"def add_values(a, b) ;TI" a + b ;TI" end ;T;0o; ;[I"OWhen called, the arguments must be provided in the exact order. In other ;TI")words, the arguments are positional.;T@ S; ; i; I"Default Values;T@ o; ;[I"'Arguments may have default values:;T@ o;;[I"def add_values(a, b = 1) ;TI" a + b ;TI" end ;T;0o; ;[I"RThe default value does not need to appear first, but arguments with defaults ;TI"+must be grouped together. This is ok:;T@ o;;[I"%def add_values(a = 1, b = 2, c) ;TI" a + b + c ;TI" end ;T;0o; ;[I"#This will raise a SyntaxError:;T@ o;;[I"%def add_values(a = 1, b, c = 1) ;TI" a + b + c ;TI" end ;T;0S; ; i; I"Array Decomposition;T@ o; ;[I"LYou can decompose (unpack or extract values from) an Array using extra ;TI""parentheses in the arguments:;T@ o;;[ I"def my_method((a, b)) ;TI" p a: a, b: b ;TI" end ;TI" ;TI"my_method([1, 2]) ;T;0o; ;[I"This prints:;T@ o;;[I"{:a=>1, :b=>2} ;T;0o; ;[I"JIf the argument has extra elements in the Array they will be ignored:;T@ o;;[ I"def my_method((a, b)) ;TI" p a: a, b: b ;TI" end ;TI" ;TI"my_method([1, 2, 3]) ;T;0o; ;[I"'This has the same output as above.;T@ o; ;[I"SYou can use a * to collect the remaining arguments. This splits ;TI"0an Array into a first element and the rest:;T@ o;;[ I"def my_method((a, *b)) ;TI" p a: a, b: b ;TI" end ;TI" ;TI"my_method([1, 2, 3]) ;T;0o; ;[I"This prints:;T@ o;;[I"{:a=>1, :b=>[2, 3]} ;T;0o; ;[I"QThe argument will be decomposed if it responds to #to_ary. You should only ;TI"Ddefine #to_ary if you can use your object in place of an Array.;T@ o; ;[I"OUse of the inner parentheses only uses one of the sent arguments. If the ;TI"Oargument is not an Array it will be assigned to the first argument in the ;TI"Rdecomposition and the remaining arguments in the decomposition will be +nil+:;T@ o;;[ I"!def my_method(a, (b, c), d) ;TI" p a: a, b: b, c: c, d: d ;TI" end ;TI" ;TI"my_method(1, 2, 3) ;T;0o; ;[I"This prints:;T@ o;;[I"${:a=>1, :b=>2, :c=>nil, :d=>3} ;T;0o; ;[I",You can nest decomposition arbitrarily:;T@ o;;[I" def my_method(((a, b), c)) ;TI" # ... ;TI" end ;T;0S; ; i; I"Array/Hash Argument;T@ o; ;[I"TPrefixing an argument with * causes any remaining arguments to be ;TI"converted to an Array:;T@ o;;[ I"&def gather_arguments(*arguments) ;TI" p arguments ;TI" end ;TI" ;TI"1gather_arguments 1, 2, 3 # prints [1, 2, 3] ;T;0o; ;[I"TThe array argument must be the last positional argument, it must appear before ;TI"any keyword arguments.;T@ o; ;[I"TThe array argument will capture a Hash as the last entry if a hash was sent by ;TI"/the caller after all positional arguments.;T@ o;;[I"4gather_arguments 1, a: 2 # prints [1, {:a=>2}] ;T;0o; ;[I"THowever, this only occurs if the method does not declare any keyword arguments.;T@ o;;[ I"=def gather_arguments_keyword(*positional, keyword: nil) ;TI"1 p positional: positional, keyword: keyword ;TI" end ;TI" ;TI"-gather_arguments_keyword 1, 2, three: 3 ;TI"8#=> raises: unknown keyword: three (ArgumentError) ;T;0o; ;[I"KAlso, note that a bare * can be used to ignore arguments:;T@ o;;[I"def ignore_arguments(*) ;TI" end ;T;0S; ; i; I"Keyword Arguments;T@ o; ;[I"OKeyword arguments are similar to positional arguments with default values:;T@ o;;[I")def add_values(first: 1, second: 2) ;TI" first + second ;TI" end ;T;0o; ;[I"GArbitrary keyword arguments will be accepted with **:;T@ o;;[ I".def gather_arguments(first: nil, **rest) ;TI" p first, rest ;TI" end ;TI" ;TI"4gather_arguments first: 1, second: 2, third: 3 ;TI"-# prints 1 then {:second=>2, :third=>3} ;T;0o; ;[I"RWhen calling a method with keyword arguments the arguments may appear in any ;TI"Sorder. If an unknown keyword argument is sent by the caller an ArgumentError ;TI"is raised.;T@ o; ;[I"LWhen mixing keyword arguments and positional arguments, all positional ;TI"8arguments must appear before any keyword arguments.;T@ S; ; i; I"Block Argument;T@ o; ;[I"JThe block argument is indicated by & and must come last:;T@ o;;[I"def my_method(&my_block) ;TI" my_block.call(self) ;TI" end ;T;0o; ;[I"RMost frequently the block argument is used to pass a block to another method:;T@ o;;[I"def each_item(&block) ;TI" @items.each(&block) ;TI" end ;T;0o; ;[ I"RIf you are only going to call the block and will not otherwise manipulate it ;TI"Oor send it to another method using yield without an explicit ;TI"Rblock parameter is preferred. This method is equivalent to the first method ;TI"in this section:;T@ o;;[I"def my_method ;TI" yield self ;TI" end ;T;0o; ;[ I"OThere is also a performance benefit to using yield over a calling a block ;TI"Rparameter. When a block argument is assigned to a variable a Proc object is ;TI"Ncreated which holds the block. When using yield this Proc object is not ;TI" created.;T@ o; ;[I"RIf you only need to use the block sometimes you can use Proc.new to create a ;TI"Sproc from the block that was passed to your method. See Proc.new for further ;TI" details.;T@ S; ; i; I"Exception Handling;T@ o; ;[I"PMethods have an implied exception handling block so you do not need to use ;TI"2+begin+ or +end+ to handle exceptions. This:;T@ o;;[ I"def my_method ;TI" begin ;TI", # code that may raise an exception ;TI" rescue ;TI" # handle exception ;TI" end ;TI" end ;T;0o; ;[I"May be written as:;T@ o;;[ I"def my_method ;TI"* # code that may raise an exception ;TI" rescue ;TI" # handle exception ;TI" end ;T;0o; ;[I"VIf you wish to rescue an exception for only part of your method, use +begin+ and ;TI"9+end+. For more details see the page on {exception ;TI"0handling}[rdoc-ref:syntax/exceptions.rdoc].;T: @file@:0@omit_headings_from_table_of_contents_below0