| Revision as of 19:02, 14 May 2014 editSmithph (talk | contribs)68 edits The archaic projection of booleans into integers is at best confusing and irrelevant.← Previous edit |
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#REDIRECT ] |
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The '''spaceship operator''', written <code><=></code>, is a binary ] that originated in the ] ]. Other languages, such as ] and ], also support the spaceship operator. Unlike traditional equality operators, which will return true or 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 ]), the operator returns <code>undef</code>. |
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{{Redirect category shell|1= |
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As a formula: |
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{{R to section}} |
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:<math> |
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{{R with history}} |
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a\ \texttt{<=>}\ b\ \ \ = |
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}} |
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\begin{cases} |
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-1 & \mbox{if }a < b, \\ |
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0 & \mbox{if }a = b, \\ |
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1 & \mbox{if }a > b, \\ |
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\texttt{undef} |
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& \mbox{otherwise.} |
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\end{cases} |
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</math> |
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In Perl, the <code><=></code> operator only performs numeric comparisons. For string-based comparison, the analogous <code>cmp</code> operator is used instead. |
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In other languages (like PHP and C) the <code><=></code> operator is not needed for numbers because one can simply do <code>b - a</code>. Rather than returning exactly 1 (or -1), this will return a value greater (or less) than 0. But for those languages this doesn't matter and works fine. |
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The spaceship operator is primarily used for comparisons in ]. |
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The spaceship operator takes its name because it resembles ]'s fighter from ] . The term is now commonly used and the operator is referred by the name within the Perl ]. |
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This operator is also used in ]-based mathematical notation to represent "less than, equal to or greater than", and is synonymous with the symbols {{unicode|⋛}} and {{unicode|⋚}}. It can be used to test if the result of a calculation is actually a number. |
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== Example == |
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<source lang="perl"> |
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$a = 5 <=> 7; # $a is set to -1 |
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$a = 7 <=> 5; # $a is set to 1 |
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$a = 6 <=> 6; # $a is set to 0 |
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</source> |
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== See also == |
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* ] |
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* ] |
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==External links== |
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{{wikibooks|Perl Programming}} |
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* |
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* |
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] |
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] |
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