Question

Does anyone know what parsing or precedence decisions resulted in the warning ‘Use of “shift” without parentheses is ambiguous’ being issued for code like:

shift . 'some string';

# and not

(shift) . 'some string'; # or
shift() . 'some string';

Is this intentional to make certain syntactic constructs easier? Or is it merely an artifact of the way perl’s parser works?

Note: this is a discussion about language design, not a place to suggest

"@{[shift]}some string"

Answer 1

With use diagnostics, you get the helpful message:

    Warning: Use of "shift" without parentheses is ambiguous at (eval
        9)[/usr/lib/perl5/5.8/perl5db.pl:628] line 2 (#1)
    (S ambiguous) You wrote a unary operator followed by something that
    looks like a binary operator that could also have been interpreted as a
    term or unary operator.  For instance, if you know that the rand
    function has a default argument of 1.0, and you write

        rand + 5;

    you may THINK you wrote the same thing as

        rand() + 5;

    but in actual fact, you got

        rand(+5);

    So put in parentheses to say what you really mean.

The fear is you could write something like shift .5 and it will be parsed like shift(0.5).