NAME

Raku port of Perl's shift() / unshift() built-ins

SYNOPSIS

use P5shift;

say shift;  # shift from @*ARGS, if any

sub a { dd @_; dd shift; dd @_ }; a 1,2,3;
[1, 2, 3]
1
[2, 3]

my @a = 1,2,3;
say unshift @a, 42;  # 4

DESCRIPTION

This module tries to mimic the behaviour of Perl's shift and unshift built-ins as closely as possible in the Raku Programming Language.

ORIGINAL PERL DOCUMENTATION

shift ARRAY
shift EXPR
shift   Shifts the first value of the array off and returns it, shortening
        the array by 1 and moving everything down. If there are no
        elements in the array, returns the undefined value. If ARRAY is
        omitted, shifts the @_ array within the lexical scope of
        subroutines and formats, and the @ARGV array outside a subroutine
        and also within the lexical scopes established by the "eval
        STRING", "BEGIN {}", "INIT {}", "CHECK {}", "UNITCHECK {}", and
        "END {}" constructs.

        Starting with Perl 5.14, "shift" can take a scalar EXPR, which
        must hold a reference to an unblessed array. The argument will be
        dereferenced automatically. This aspect of "shift" is considered
        highly experimental. The exact behaviour may change in a future
        version of Perl.

        To avoid confusing would-be users of your code who are running
        earlier versions of Perl with mysterious syntax errors, put this
        sort of thing at the top of your file to signal that your code
        will work only on Perls of a recent vintage:

            use 5.014;  # so push/pop/etc work on scalars (experimental)

        See also "unshift", "push", and "pop". "shift" and "unshift" do
        the same thing to the left end of an array that "pop" and "push"
        do to the right end.

unshift ARRAY,LIST
unshift EXPR,LIST
        Does the opposite of a "shift". Or the opposite of a "push",
        depending on how you look at it. Prepends list to the front of the
        array and returns the new number of elements in the array.

            unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;

        Note the LIST is prepended whole, not one element at a time, so
        the prepended elements stay in the same order. Use "reverse" to do
        the reverse.

        Starting with Perl 5.14, "unshift" can take a scalar EXPR, which
        must hold a reference to an unblessed array. The argument will be
        dereferenced automatically. This aspect of "unshift" is considered
        highly experimental. The exact behaviour may change in a future
        version of Perl.

        To avoid confusing would-be users of your code who are running
        earlier versions of Perl with mysterious syntax errors, put this
        sort of thing at the top of your file to signal that your code
        will work only on Perls of a recent vintage:

            use 5.014;  # so push/pop/etc work on scalars (experimental)

PORTING CAVEATS

In future language versions of Raku, it will become impossible to access the @_ variable of the caller's scope, because it will not have been marked as a dynamic variable. So please consider changing:

shift;

to:

shift(@_);

or, using the subroutine as a method syntax:

@_.&shift;

AUTHOR

Elizabeth Mattijsen [email protected]

Source can be located at: https://github.com/lizmat/P5shift . Comments and Pull Requests are welcome.

COPYRIGHT AND LICENSE

Copyright 2018, 2019, 2020, 2021 Elizabeth Mattijsen

Re-imagined from Perl as part of the CPAN Butterfly Plan.

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.