Rank (computer programming): Difference between revisions

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{{UnreferencedMore stub|auto=yescitation needed|date=DecemberFebruary 20092025}}

In [[computer programming]], '''rank''' with no further specifications is usually a synonym for (or refers to) "number of dimensions";<ref>{{Cite web |title=Vocabulary_with_defintions |url=https://files.schudio.com/federation-of-boldmere-schools/files/documents/Vocabulary_with_defintions.docx}}</ref> thus, a bitwo-dimensional array has rank ''two'', a three-dimensional array has rank ''three'' and so on.

Strictly, no formal definition can be provided which applies to every [[programming language]], since each of them has its own concepts, [[Formal semantics of programming languages|semantics]] and terminology; the term may not even be applicable or, to the contrary, applied with a very specific meaning in the context of a given language.

In the case of [[APL programming language|APL]] the notion applies to every operand; and [[Binary function|dyad]]s ("binary functions") have a ''left rank'' and a ''right rank''.

The box below instead shows how ''rank of a type'' and ''rank of an array expression'' could be defined (in a semi-formal style) for C++ and illustrates a simple way to calculate them at compile time.

<sourcesyntaxhighlight lang="cpp">

#include <type_traits>

#include <cstddef>

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* it is an array; zero otherwise (which is the usual convention)

*/

template <typename tT> struct rank

{

{ static const std::size_t value = 0; };

};

template<typename tT, std::size_t nN>

struct rank<tT[nN]>

{

{ static const std::size_t value = 1 + rank<tT>::value; };

};

template <typename t, std::size_t nT>

constexpr auto rank_v = rank<T>::value;

/* Rank of an expression

Line 27 ⟶ 36:

* Let the rank of an expression be the rank of its type

*/

template <typename t, std::size_t n>

template <typename T>

char(&rankof(t(&)[n]))[n];

using unqualified_t = std::remove_cv_t<std::remove_reference_t<T>>;

</source>

template <typename T>

auto rankof(T&& expr)

{

return rank_v<unqualified_t<T>>;

}

</syntaxhighlight>

Given the code above the rank of a type T can be calculated at compile time by

:<sourcesyntaxhighlight lang="cpp">rank<T>::value</sourcesyntaxhighlight>

or the shorter form

and the rank of an array-expression ''expr'' by

:<syntaxhighlight lang="cpp">rank_v<T></syntaxhighlight>

andCalculating the rank of an array-expression ''expr''can bybe done using

:<sourcesyntaxhighlight lang="cpp">sizeof(rankof(expr))</sourcesyntaxhighlight>

==See also==

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*[[Rank (J programming language)]], a concept of the same name in the [[J (programming language)|J programming language]]

== References ==

<references />{{DEFAULTSORT:Rank (Computer Programming)}}

[[Category:Arrays]]

[[Category:Programming language topics]]