Rank (computer programming)

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, 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 the notion applies to every operand; and dyads ("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.

#include /* 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 struct rank{ static const std::size_t value = 0; };

templatestruct rank{ static const std::size_t value = 1 + rank::value; };

/* Rank of an expression * * Let the rank of an expression be the rank of its type */template char(&rankof(t(&) [n] )) [n] ; Given the code above the rank of a type T can be calculated at compile time by :rank::value and the rank of an array-expression "expr" by :sizeof(rankof(expr))

ee also

*Rank (linear algebra), for a definition of "rank" as applied to matrices
*Rank (J programming language), a concept of the same name in the J programming language