Array bounds checking

davehorsfall has asked for the wisdom of the Perl Monks concerning the following question:

Most potent, grave, and reverend signiors,

Are there plans to add runtime array bounds checking some time, or perhaps someone has written a module? Such a thing would have gone a long way in helping me with nailing a problem with a 10x10 array, whereby Perl (5.16.3) happily extended rows for me when I forgot to reset the column counter.

I envisage something like:

pragma arraycheck @myarray[10][10];
[download]

to enforce under pain of death that @myarray is 10x10, and some way to enable it at runtime from the command line during development.

Ta muchly.

-- Dave

Comment on Array bounds checking Download Code

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Re: Array bounds checking by SuicideJunkie (Vicar) on Sep 09, 2014 at 19:20 UTC
Arrays don't have a fixed size, but you could make an object that stores an array and enforces its size during updates. There may already be tied arrays and such available on CPAN. Wanting a fixed-size array in the first place smells a bit odd in itself to me. What is your use case?	[reply]
Re^2: Array bounds checking by davehorsfall (Novice) on Sep 09, 2014 at 21:16 UTC
I seem to be forever coming up with odd use cases. This one is a puzzle-solver, involving a 10x10 numeric grid of 1's and 0's (Binary Brainsnack if you're familiar with it). In hindsight I probably would've chosen another data structure. -- Dave	[reply]
Re^3: Array bounds checking by AppleFritter (Vicar) on Sep 09, 2014 at 21:22 UTC
In hindsight I probably would've chosen another data structure. It's never too late to refactor your code.	[reply]
Re: Array bounds checking by Laurent_R (Canon) on Sep 09, 2014 at 21:20 UTC
The fact that arrays can grow to fit your needs is just one of the really great things with dynamic languages in general and with Perl in particular: no need to keep track of the size and to malloc new memory chunks. Now, having said that, if you want to implement such a limitation, it is quite easy to do it: just don't access directly to your arrays, but do it through a small set of functions that check for bounds and return an exception when your program gets off-limits. So you could implement special versions of `push`, `unshift` to check bounds, as well as a `set_val` and a `get_val` mutator and accessor functions to access to the array elements. Although I am not a great fan of OO programming in general, this is one case where it really makes sense and I might very probably implement it as an object-oriented module to create and manage arrays through a bunch of methods. (Or, perhaps, I would be tempted to do it with some closures, this usually makes it possible to do the thing in probably twice less code compared to OO code, but that's a different question and a matter of purely personal inclination.) As mentioned by other monks before, a tied array might be a more transparent solution, but I haven't been really convinced so far by tied arrays and hashes.	[reply] [d/l] [select]
Re: Array bounds checking by LanX (Saint) on Sep 09, 2014 at 19:32 UTC
If there is not already a module on cpan (which I doubt) you could implement it with Tie::Array . Overwriting EXTEND () looks like the best approach. Be warned about the performance loss involved when using tie. Try searching cpan for other solutions. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)}	[reply]
Re^2: Array bounds checking by davehorsfall (Novice) on Sep 09, 2014 at 21:20 UTC
Thanks; I'll take a look at it. -- Dave	[reply]
Re: Array bounds checking by GrandFather (Saint) on Sep 09, 2014 at 22:41 UTC
It's already been hinted that you could solve this with an OO solution. Actually, I'd have started with the board implemented as an object just so I could hide the "under the hood" board representation details and manipulate it at a high level that makes it easy to separate the puzzle solving logic from the board manipulation code. Perl is the programming world's equivalent of English	[reply]