In computer science, a relational operator is a programming language construct or operator that tests or defines some kind of relation between two entities. These include numerical equality and inequalities...
Perl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
Ruby is a dynamic, reflective, general-purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features. Ruby originated in Japan during the mid-1990s and was first developed and designed by Yukihiro "Matz" Matsumoto...
and Groovy also support the spaceship operator. Unlike traditional equality operators, which will return 1 (true) or 0 (false) depending on whether the arguments are equal or unequal, the spaceship operator will return 1, 0, or −1 depending on the value of the left argument relative to the right argument. If the left argument is greater than the right argument, the operator returns 1. If the left argument is less than the right argument, the operator returns −1. If the two arguments are equal, the operator returns 0. If the two arguments cannot be compared (e.g. one of them is NaN
NaN
In computing, NaN is a value of the numeric data type representing an undefined or unrepresentable value, especially in floating-point calculations...
), the operator returns undef.
In Perl, the <=> operator only performs numeric comparisons. For string-based comparison, the analogous cmp operator is used instead.
As a formula:
The spaceship operator is primarily used for comparisons in sorting
Sorting
Sorting is any process of arranging items in some sequence and/or in different sets, and accordingly, it has two common, yet distinct meanings:# ordering: arranging items of the same kind, class, nature, etc...
.
The spaceship operator takes its name because it looks like a small flying saucer
Flying saucer
A flying saucer is a type of unidentified flying object sometimes believed to be of alien origin with a disc or saucer-shaped body, usually described as silver or metallic, occasionally reported as covered with running lights or surrounded with a glowing light, hovering or moving rapidly either...
ASCII art is a graphic design technique that uses computers for presentation and consists of pictures pieced together from the 95 printable characters defined by the ASCII Standard from 1963 and ASCII compliant character sets with proprietary extended characters...
. The term is now commonly used and the operator is referred by the name within the Perl documentation
Plain Old Documentation
Plain Old Documentation, abbreviated pod, is a lightweight markup language used to document the Perl programming language.-Design:pod is designed to be a simple, clean language with just enough syntax to be useful. It purposefully does not include mechanisms for fonts, images, colors or tables...
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
-based mathematical notation to represent "less than, equal to or greater than", and is synonymous with the symbols and . It can be used to test if the result of a calculation is actually a number.
Example
$a = 5 <=> 7; # $a is set to -1
$a = 7 <=> 5; # $a is set to 1
$a = 6 <=> 6; # $a is set to 0
