Symbol (programming): Difference between revisions

Revision as of 04:53, 5 July 2011

Revision as of 03:33, 10 July 2011

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A '''symbol''' in [[computer programming]] is a primitive [[datatype]] whose [[instance]]s have a unique human-readable form. Symbols can be used as [[identifiers]]. In some [[programming languages]], that are called '''atoms'''<ref name=pickaxe>{{cite book|last=Hunt|first=Dave Thomas ; Chad Fowler ; Andy|title=Programming Ruby the pragmatic programmers' guide ; [includes Ruby 1.8]|year=2001|publisher=The Pragmatic Bookshelf|___location=Raleigh, NC|isbn=978-0974514055|url=http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html|edition=2. ed., 10. print.}}</ref>.

In the most trivial [[implementation]], they are essentially named [[integer]]s.

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| [[Ericsson]] [[Erlang (programming language)|Erlang]] || ? || <tt>sym</tt>

|}

=== Lisp ===

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<source lang="lisp">

package:exported-symbol

</source>

===Ruby===

In [[Ruby (programming language)|Ruby]], symbols can be created with a literal form, or by converting a string<ref name=pickaxe />.

They can be used as an identifier or an interned string<ref name=rubysymbol>{{cite web|last=Kidd|first=Eric|title=13 Ways of Looking at a Ruby Symbol|url=http://www.randomhacks.net/articles/2007/01/20/13-ways-of-looking-at-a-ruby-symbol#9|work=Random Hacks|accessdate=10 July 2011}}</ref>.

It is considered a [[best practice]] to use symbols as keys to an [[associative array]] in Ruby<ref name=rubysymbol /><ref name=wrongreason>{{cite web|title=Using Symbols for the Wrong Reason|url=http://microjet.ath.cx/WebWiki/2005.12.27_UsingSymbolsForTheWrongReason.html|work=Gnomic Notes}}</ref>.

====Examples====

The following is a simple example of a symbol literal in Ruby<ref name=pickaxe />:

<source lang=ruby>

my_symbol = :a

my_symbol = :"a"

</source>

Symbols can be [[String interpolation|interpolated]]:

<source lang=ruby>

money = :"#{2+3} dollars" #=> :"5 dollars"

print "I have #{money}" #=> "I have 5 dollars"

</source>

Strings can be coerced into symbols, vice versa:

<source lang=ruby>

my_symbol = "Hello, world!".intern #=> :"Hello, world!"

my_symbol = "Hello, world!".to_sym #=> :"Hello, world!"

my_string = :hello.to_s

</source>

Symbols are objects of the <code>Symbol</code> class in Ruby<ref name=rdocsymbol>{{cite web|title=Symbol|url=http://www.ruby-doc.org/core/classes/Symbol.html|work=Ruby Documentation|accessdate=10 July 2011}}</ref>:

<source lang=ruby>

my_symbol = :hello_world

my_symbol.length #=> 11

my_symbol.class #=> Symbol

my_symbol.to_s.reverse.to_sym #=> :dlrow_olleh

</source>

Symbols as keys of an associative array:

<source lang=ruby>

my_hash = { a: "apple", b: "banana" }

my_hash[:a] #=> "apple"

my_hash[:b] #=> "banana"

</source>

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[[Category:Lisp programming language]]

[[Category:Ruby programming language]]

[[Category:Articles with example Ruby code]]

[[Category:Programming constructs]]

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