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

Revision as of 07:30, 5 March 2021

Revision as of 02:14, 7 March 2021

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===Erlang===

[[Erlang (programming language)|Erlang]] offers many ways to represent mappings; twothree of the most common in the standard library are keylists, dictionaries, and dictionariesmaps.

====Keylists====

Keylists are lists of tuples[[tuple]]s, where the first element of each [[tuple]] is a key, and the second is a value. Functions for operating on keylists are provided in the <code>lists</code> module.

<syntaxhighlight lang=Erlang>

PhoneBook = [{"Sally SmartSmith", "555-9999"},

{"John Doe", "555-1212"},

{"J. Random Hacker", "553-1337"}].

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<syntaxhighlight lang=Erlang>

{_, Phone} = lists:keyfind("Sally SmartSmith", 1, PhoneBook),

io:format("Phone number: ~s~n", [Phone]).

</syntaxhighlight>

====Dictionaries====

Dictionaries are implemented in the <code>dict</code> module of the standard library. A new dictionary is created using the <code>dict:new/0</code> function and new key/value pairs are stored using the <code>dict:store/3</code> function:

<syntaxhighlight lang=Erlang>

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<syntaxhighlight lang=Erlang>

PhoneBook = dict:from_list([{"Sally Smith", "555-9999"},
{"John Doe", "555-1212"},

{"J. Random Hacker", "553-1337"}]).

</syntaxhighlight>

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In both cases, any Erlang term can be used as the key. Variations include the <code>orddict</code> module, implementing ordered dictionaries, and <code>gb_trees</code>, implementing general balanced trees.

====Maps====

Maps were introduced in OTP 17.0,<ref>{{Cite web|title=Erlang -- maps|url=https://erlang.org/doc/man/maps.html|access-date=2021-03-07|website=erlang.org}}</ref> and combine the strengths of keylists and dictionaries. A map is defined using the syntax <code>#{ K1 => V1, ... Kn => Vn }</code>:

<syntaxhighlight lang=Erlang>

PhoneBook = #{"Sally Smith" => "555-9999",

"John Doe" => "555-1212",

"J. Random Hacker" => "553-1337"}.

</syntaxhighlight>

Basic functions to interact with maps are available from the <code>maps</code> module. For example, the <code>maps:find/2</code> function returns the value associated with a key:

<syntaxhighlight lang=Erlang>

{ok, Phone} = maps:find("Sally Smith", PhoneBook),

io:format("Phone: ~s~n", [Phone]).

</syntaxhighlight>

Unlike dictionaries, maps can be pattern matched upon:

<syntaxhighlight lang=Erlang>

#{"Sally Smith", Phone} = PhoneBook,

io:format("Phone: ~s~n", [Phone]).

</syntaxhighlight>

Erlang also provides syntax sugar for functional updates—creating a new map based on an existing one, but with modified values or additional keys:

<syntaxhighlight lang=Erlang>

PhoneBook2 = PhoneBook#{

% the `:=` operator updates the value associated with an existing key

"J. Random Hacker" := "355-7331",

% the `=>` operator adds a new key-value pair, potentially replacing an existing one

"Alice Wonderland" => "555-1865"

}

</syntaxhighlight>

===F#===