Comparison of programming languages (associative array): Difference between revisions

Revision as of 01:44, 16 July 2023

Revision as of 11:42, 10 August 2023

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Just "555-1212"

Lists of pairs and functional maps both provide a purely functional interface, which is more idiomatic in Haskell. In contrast, hash tables provide an imperative interface in the [[Monad_Monad (functional_programmingfunctional programming)#IO_monadIO monad|IO monad]].

===Java===

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delete!(phonebook, "Sally Smart")

Get keys and values as [[Iterator#Implicit_iteratorsImplicit iterators|iterables]]:

keys(phonebook)

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</syntaxhighlight>

In Mac OS X 10.5+ and iPhone OS, dictionary keys can be enumerated more concisely using the <code>NSFastEnumeration</code> construct:<ref>{{cite web |title=NSFastEnumeration Protocol Reference |url=https://developer.apple.com/documentation/Cocoa/Reference/NSFastEnumeration_protocol/ |date=2011 |archive-url=https://web.archive.org/web/20160313082808/https://developer.apple.com/library/mac/documentation/Cocoa/Reference/NSFastEnumeration_protocol/ |archive-date=13 March 2016 |website=Mac Developer Library |access-date=3 August 2020}}</ref>

<syntaxhighlight lang=ObjC>

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</syntaxhighlight>

Accessing a hash element uses the syntax <code>$hash_name{$key}</code> – the key is surrounded by [[Bracket#Curly_bracketCurly bracket|curly braces]] and the hash name is prefixed by a <code>$</code>, indicating that the hash element itself is a scalar value, even though it is part of a hash. The value of <code>$phone_book{'John Doe'}</code> is <code>'555-1212'</code>. The <code>%</code> sigil is only used when referring to the hash as a whole, such as when asking for <code>keys %phone_book</code>.

The list of keys and values can be extracted using the built-in functions <code>keys</code> and <code>values</code>, respectively. So, for example, to print all the keys of a hash:

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===PHP===

[[PHP]]'s built-in array type is, in reality, an associative array. Even when using numerical indexes, PHP internally stores arrays as associative arrays.<ref>About the implementation of [http://se.php.net/manual/en/language.types.array.php Arrays] in PHP</ref> So, PHP can have non-consecutively numerically- indexed arrays. The keys have to be of integer (floating point numbers are truncated to integer) or string type, while values can be of arbitrary types, including other arrays and objects. The arrays are heterogeneous: a single array can have keys of different types. PHP's associative arrays can be used to represent trees, lists, stacks, queues, and other common data structures not built into PHP.

An associative array can be declared using the following syntax: