Editing Rank (computer programming)

{{More citation needed|date=February 2025}}

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 two-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.

<syntaxhighlight lang="cpp">
#include <type_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 T> struct rank
{
    static const std::size_t value = 0;
};

template<typename T, std::size_t N>
struct rank<T[N]>
{
    static const std::size_t value = 1 + rank<T>::value;
};

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

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

template <typename T>
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
 
:<syntaxhighlight lang="cpp">rank<T>::value</syntaxhighlight>
 
or the shorter form

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

Calculating the rank of an expression can be 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)}}
[[Category:Arrays]]
[[Category:Programming language topics]]


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