@nogc vs IAllocator

[Lodovico Giaretta via Digitalmars-d]

Background: working on a replacement for std.xml. Designing the 
DOM API.

Of course, I have to provide a way for the users to use a custom 
allocator for the DOM objects.

But the DOM, as described in the official docs[1] (and as I would 
like to have it), shall be pluggable: many implementation may be 
available, and the user can ask for one that provides the 
extensions ("features" in the DOM spec) that he needs. This kind 
of OOP, with various implementation providers, does not work well 
with templates, so the "D way" of having a template parameter for 
the allocator is quite complex and ugly.

The "standard DOM way" of dealing with any additional thing (as 
is the allocator selection) is to use hasFeature/getFeature; this 
are standard OOP interface methods, so the work very very well 
with IAllocator, thus allowing an easy, straightforward solution. 
But this solution is not @nogc (as IAllocator has no information 
of what the underlying implementation is).

So my question is: which solution should I use:
1) a template based solution, which for this problem looks like 
an hack, so then I can say "Phobos provides a full DOM Level 3 
implementation that works in @nogc code"
2) a standard OOP solution, very DOM style, but then I have to 
say "Phobos provides a full DOM Level 3 implementation that does 
not use the GC, but cannot be marked @nogc; if you don't trust 
me, check the profiler"

Thank you in advance for your help on this matter!