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Programming Ruby

The Pragmatic Programmer's Guide
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class Struct
Parent: Object
Version: 1.6

Index:

new new members == [ ] [ ]= each length members size to_a values


Subclasses: Struct::Tms

A Struct is a convenient way to bundle a number of attributes together, using accessor methods, without having to write an explicit class.

The Struct class is a generator of specific classes, each one of which is defined to hold a set of variables and their accessors. In these examples, we'll call the generated class ``CustomerClass,'' and we'll show an example instance of that class as ``CustomerInst.''

In the descriptions that follow, the parameter aSymbol refers to a symbol, which is either a quoted string or a Symbol (such as :name).
mixins
Enumerable: collect, detect, each_with_index, entries, find, find_all, grep, include?, map, max, member?, min, reject, select, sort, to_a

class methods
new Struct.new( [ aString ] [, aSym ]+ ) -> CustomerClass

Creates a new class, named by aString, containing accessor methods for the given symbols. If the name aString is omitted, an anonymous structure class will be created. Otherwise, the name of this struct will appear as a constant in class Struct, so it must be unique for all Structs in the system and should start with a capital letter.

Struct.new returns a new Class object, which can then be used to create specific instances of the new structure. The remaining methods listed below (class and instance) are defined for this generated class. See the description that follows for an example.

new CustomerClass.new( [ anObject ]+ ) -> CustomerInst

Creates a new instance. The number of actual parameters must be less than or equal to the number of attributes defined for this class; unset parameters default to nil. Passing too many parameters will raise an ArgumentError.

Customer = Struct.new( "Customer", :name, :address, :zip )
joe = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joe.name » "Joe Smith"
joe.zip » 12345

members CustomerClass.members -> anArray

Returns an array of strings representing the names of the instance variables.

Customer = Struct.new( "Customer", :name, :address, :zip )
Customer.members » ["name", "address", "zip"]

instance methods
== CustomerInst == anOtherStruct -> true or false

Equality---Returns true if anOtherStruct is equal to this one: they must be of the same class as generated by Struct.new , and the values of all instance variables must be equal (according to Object#== ).

Customer = Struct.new( "Customer", :name, :address, :zip )
joe   = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joejr = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
jane  = Customer.new( "Jane Doe", "456 Elm, Anytown NC", 12345 )
joe == joejr » true
joe == jane » false

[ ] CustomerInst[ aSymbol ] -> anObject
CustomerInst[ anInteger ] -> anObject

Attribute Reference---Returns the value of the instance variable named by aSymbol, or indexed (0..length-1) by anInteger. Will raise NameError if the named variable does not exist, or IndexError if the index is out of range.

Customer = Struct.new( "Customer", :name, :address, :zip )
joe = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joe["name"] » "Joe Smith"
joe[:name] » "Joe Smith"
joe[0] » "Joe Smith"

[ ]= CustomerInst[ aSymbol ] = anObject -> anObject
CustomerInst[ anInteger ] = anObject -> anObject

Attribute Assignment---Assigns to the instance variable named by aSymbol or anInteger the value anObject and returns it. Will raise a NameError if the named variable does not exist, or an IndexError if the index is out of range.

Customer = Struct.new( "Customer", :name, :address, :zip )
joe = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joe["name"] = "Luke"
joe[:zip]   = "90210"
joe.name » "Luke"
joe.zip » "90210"

each CustomerInst.each {| anObject | block }

-> CustomerInst

Calls block once for each instance variable, passing the value as a parameter. 

Customer = Struct.new( "Customer", :name, :address, :zip )
joe = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joe.each {|x| puts(x) }
produces: 
Joe Smith
123 Maple, Anytown NC
12345

length CustomerInst.length -> anInteger

Returns the number of instance variables.

Customer = Struct.new( "Customer", :name, :address, :zip )
joe = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joe.length » 3

members CustomerInst.members -> anArray

Returns an array of strings representing the names of the instance variables.

Customer = Struct.new( "Customer", :name, :address, :zip )
joe = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joe.members » ["name", "address", "zip"]

size CustomerInst.size -> anInteger

Synonym for Struct#length .

to_a CustomerInst.to_a -> anArray

Returns the values for this instance as an array.

Customer = Struct.new( "Customer", :name, :address, :zip )
joe = Customer.new( "Joe Smith", "123 Maple, Anytown NC", 12345 )
joe.to_a[1] » "123 Maple, Anytown NC"

values CustomerInst.values -> anArray

Synonym for to_a.

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Extracted from the book "Programming Ruby - The Pragmatic Programmer's Guide"
Copyright © 2001 by Addison Wesley Longman, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/)).

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