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In [[computer programming]], '''rank''' with no further specifications is usually a synonym for (or refers to) "number of dimensions"; thus, for instance, a bi-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 [[computer programming]], '''rank''' with no further specifications is usually a synonym for (or refers to) "number of dimensions";<ref>{{Cite thus,web for|title=Vocabulary_with_defintions instance|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.

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

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 [[dyadBinary function|dyadsdyad]]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.

<syntaxhighlight lang="cpp">

<code>

#include <cstddeftype_traits>

#include <cstddef>

//* Rank of a type

//* -------------

//*

//* Let the 'rank' of a type T be the number of its dimensions if

//* 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 t, std::size_t n>

struct rank<t[n]>

{template<typename static constT, std::size_t value = 1 + rank<tN>::value; };

struct rank<tT[nN]>

{

// Rank of an expression

static const std::size_t value = 1 + rank<T>::value;

//

};

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

//

template <typename t, std::size_t nT>

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

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

</code>

//* Rank of an expression

*

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

/*/

template <typename t, std::size_t nT>

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

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

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

or the shorter form

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

:<code>sizeof(rankof(expr))</code>

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

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

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

==See also==

*[[Rank (linear algebra)]], for a definition of ''rank'' as applied to [[matrix (mathematics)|matrices]]

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

== References ==

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

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