Re: [Parseperl-discuss] Performance hacks

[Adam K. <ad...@ph...>]

>> my $doc = PPI::Document->new( $something,
>>     readonly => 1,
>>     );
> 
> I was thinking something quite similar earlier today, but I couldn't 
> think of a good way to implement it without either 1) sprinkling "if 
> ($self->top->readonly)" everywhere, or 2) multiple inheritance or mixin 
> of a ::Mutable class for the non-readonly case.

Agreed, actually checking it in every ->prune call would be onerous and 
slow things down, and doing some form of mutation or mixin for 
non-read-only seems infeasible without having entire seperate trees, 
tripling the number of classes. :/

 > Wait, are you suggesting a global readonly flag, or a per-instance
 > readonly?  It sounds like the former.  I was instead thinking of the
 > latter.

What I'm thinking is that we make ->readonly an advisory flag.

If you create with ->readonly, then at least we (or anyone else) can 
know that the document as a whole is _intended_ to be readonly.

We might not actually enforce it at the add_before level, but it can be 
checked in all sorts of places like PPI::Transform and so on, that deal 
with entire documents.

It means at least anything that cares about readonly has the option to 
look for it.

It also means we can then IN ADDITION to the advisory ->readonly 
attribute, we can implement a global ReadOnly mode to modify the 
function undef PPI::...

Once that global ReadOnly is enabled, PPI::Document->new would simply 
die or return undef, and refuse to allow any document to be created that 
_doesn't_ have the ->readonly flag.

So it would be a partly-cooperative, partly-enforced concept.

Enforced at the per-document level, but cooperative at the per-element 
level. Because indeed doing ->top->readonly all over the place would be 
fairly hideous and slow things down (although we can look at adding it 
down the line).

Adam K