Bug #118305 for Moose: Array map/grep method allows to change value without constraint check

Sat Oct 08 19:53:40 2016 happy.barney [...] gmail.com - Ticket created

Subject:	Array map/grep method allows to change value without constraint check
Date:	Sun, 9 Oct 2016 01:53:31 +0200
To:	bug-Moose [...] rt.cpan.org
From:	Branislav Zahradník <happy.barney [...] gmail.com>

If code passed to native trait map/grep assigns value to $_, value is stored but constraints are not verified. Snippet: package Foo; has list => is => 'ro', isa => 'ArrayRef[Defined]', handles => { map => 'map' }; Usage; my $foo = Foo->new( list => [1 .. 10] ); $foo->map( sub { $_ = undef } ); Solution: return 'map { local $_ = $_; $_[0]->() } @{ (' . $slot_access . ') }'; Best regards, Branislav Zahradník

Sat Oct 08 20:01:34 2016 ether [...] cpan.org - Correspondence added

On 2016-10-08 16:53:40, happy.barney@gmail.com wrote: Show quoted text

> If code passed to native trait map/grep assigns value to $_, value is > stored but constraints are not verified.

I don't think this is fixable. You're altering the contents of the array elements via a reference. Moose can't see what you're doing there, so you can change the values to anything. The only alternative is to make a full copy of the list before allowing you to traverse it, which would get expensive.

Sat Oct 08 20:01:35 2016 The RT System itself - Status changed from 'new' to 'open'

Sat Oct 08 20:19:33 2016 happy.barney [...] gmail.com - Correspondence added

Subject:	Re: [rt.cpan.org #118305] Array map/grep method allows to change value without constraint check
Date:	Sun, 9 Oct 2016 02:19:24 +0200
To:	bug-Moose [...] rt.cpan.org
From:	Branislav Zahradník <happy.barney [...] gmail.com>

well, that's true, if element is a reference, there is no chance to detect it except rewrite map to Writer. using "local $_ = $_" prevents at least assign to $_ changes (often unintended) On 9 October 2016 at 02:01, Karen Etheridge via RT <bug-Moose@rt.cpan.org> wrote: Show quoted text

> <URL: https://rt.cpan.org/Ticket/Display.html?id=118305 > > > On 2016-10-08 16:53:40, happy.barney@gmail.com wrote:

> > If code passed to native trait map/grep assigns value to $_, value is > > stored but constraints are not verified.

> > I don't think this is fixable. You're altering the contents of the array > elements via a reference. Moose can't see what you're doing there, so you > can change the values to anything. > > The only alternative is to make a full copy of the list before allowing > you to traverse it, which would get expensive. >

Sat Oct 08 20:24:54 2016 ether [...] cpan.org - Correspondence added

On 2016-10-08 17:19:33, happy.barney@gmail.com wrote: Show quoted text

> well, that's true, if element is a reference, there is no chance to detect > it except rewrite map to Writer.

It doesn't what matter the type of the elements are. Show quoted text

> using "local $_ = $_" prevents at least assign to $_ changes (often > unintended)

Indeed. This could potentially be added as a new type of delegate accessor, but I don't think we can change the existing ones without breaking code.