Mastering Modern Perl: Writing Efficient and Maintainable Code/

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Advanced Functions

Advanced Functions

Learn about advanced functions in Perl.

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Functions are the foundation of many advanced Perl features.

Context awareness

Perl’s built-ins know whether we’ve invoked them in void, scalar, or list context. So too can our functions. The wantarray built-in returns undef to signify void context, a false value to signify scalar context, and a true value to signify list context. Yes, it’s misnamed; see perldoc -f wantarray for proof.

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Perl
sub context_sensitive {
    my $context = wantarray();
    return 'List context' if          $context;
    say 'Void context' unless defined $context;
    return 'Scalar context' unless    $context;
}
context_sensitive();
say my $scalar = context_sensitive();
say context_sensitive();

This can be useful for functions that might produce expensive return values to avoid doing so in void context. Some idiomatic functions return a list-in-list context and the first element of the list or an array reference in scalar context. However, there is no single best recommendation for the use of wantarray. Sometimes, it’s clearer to write separate and unambiguous functions, such as get_all_toppings() and get_next_topping().

Robin Houston’s Want and Damian Conway’s ...

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