Detecting Return Context
Problem
You want to know whether your function was called in scalar context or list context. This lets you have one function that does different things, like most of Perl’s built-in functions.
Solution
Use the wantarray()
function, which has three
possible return values depending on how the current function was
called:
if (wantarray()) { # list context } elsif (defined wantarray()) { # scalar context } else { # void context }
Discussion
Many built-in functions act differently when called in scalar context
than in list context. A user-defined function can learn the context
it was called in by examining the return value from the
wantarray
built-in. List context is indicated by a
true return value. If it returns a value that is false but defined,
then the function’s return value will be used in scalar
context. If it returns undef
, it isn’t being
asked to provide a value at all.
if (wantarray()) { print "In list context\n"; return @many_things; } elsif (defined wantarray()) { print "In scalar context\n"; return $one_thing; } else { print "In void context\n"; return; # nothing } mysub(); # void context $a = mysub(); # scalar context if (mysub()) { } # scalar context @a = mysub(); # list context print mysub(); # list context
See Also
The return
and wantarray
functions in Chapter 3 of Programming Perl and
perlfunc
(1)
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