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

Revision as of 17:43, 17 April 2011

Revision as of 02:45, 8 June 2011

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=== D ===

[[D programming language|D]] offers direct support for associative arrays

in the core language -– they are implemented as a chaining hash table with binary trees.<ref>{{Cite web|url=http://digitalmars.com/d/2.0/hash-map.html |title=Associative Arrays |accessdate=2011-02-01 |work= |date= }}</ref>. The equivalent example would be:

<source lang="d">

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<pre>

mapping = NEWOBJECT("Collection")

mapping.Add("Daffodils", "flower2") && Add(object, key) -– key must be character

index = mapping.GetKey("flower2") && returns the index value 1

object = mapping("flower2") && returns "Daffodils" (retrieve by key)

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["Sally Smart"] = "555-9999",

["John Doe"] = "555-1212",

["J. Random Hacker"] = "553-1337", --– Trailing comma is OK

}

aTable = {

-- Table as value

subTable = { 5, 7.5, k = true }, --– key is "subTable"

-- Function as value

['John Doe'] = function (age) if age < 18 then return "Young" else return "Old!" end end,

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</source>

Accessing a hash element uses the syntax <code>$hash_name{$key}</code> —– the key is surrounded by ''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: