I am forwarding the comment below from Jean-Damien into the group for
feedback.
My sense of the matter is that Perl methods using named argument hashes
are entitled to consume them in the process. That means that after
$hashp = { ... repeatedly useful things };
my $recognizer = Marpa::R2::Scanless::R->new($hashp);
reuse of $hashp cannot be relied on to work, because Marpa::R2's methods
may consume the hash pointed to by $hashp. (Marpa often needs to process
its arguments in stages, and finds its useful to track those already
processed by deleting elements.) Note that the user can get around this
by copying the hash, which moves the overhead for these unusual argument
manipulations from application to user, which to my mind is a good thing.
Anyone else have a sense of this matter? Simply stating your personal
preference is OK, but I'll give greater weight to evidence of best
practices, traditions, etc.
-- jeffrey
-------- Original Message --------
Subject: Re: [Marpa--R2] Work on multiple lexers: t+, but noisy (f9d2b50)
Date: Sat, 21 Dec 2013 08:00:51 -0800
From: jddurand <notificati...@github.com>
Reply-To: jeffreykegler/Marpa--R2
<reply+c-4923070-46b158946abddd67de008743caef1226be890a0d-173...@reply.github.com>
To: jeffreykegler/Marpa--R2 <marpa-...@noreply.github.com>
Playing with user's arguments has side-effects. The line:
|delete $args[0]->{grammar};
|
in particular is disastrous for callers that are storing a reference to
a precompiled grammar, not having a reference to it anywhere else in
this program than in the hash given in input to R->new().
For example, if the grammar is precompiled and referenced only in a hash
used as a R->new() parameter, then Scanless will happily destroy the
precompiled grammar.
Example with the perl6 advent calendar where I modified the arguments to
R->new(). Look to $hashp in the source code at
https://gist.github.com/jddurand/8071223
Output is:
|2♥ 5♥ 7♦ 8♣ 9♠ : OK
'grammar' name argument to scanless_r->new() is undefined
It should be a ref to Marpa::R2::Scanless::G
Marpa::R2 exception at /tmp/perl6advent.day18.with.marpa.pl line 22.
|
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