Hello WebCritters,
I’m moving some code around, and one particular header I have is included
everywhere in JSC so I’d like it to be lightweight and include as few other
headers as possible. It unfortunately uses WTF::Vector, but it only does so as
a pointer:
void ohNoes(Vector<Noms>*);
It seems like something a forward declaration would fix nicely, and oh joy and
wonder we have Forward.h just for this! Here’s what it does:
template<typename T, size_t inlineCapacity, typename OverflowHandler, size_t
minCapacity, typename Malloc> class Vector;
That’s nice and great for T, but all the other template parameters are SOL
because Vector is actually declared with default template parameters:
template<typename T, size_t inlineCapacity = 0, typename OverflowHandler =
CrashOnOverflow, size_t minCapacity = 16, typename Malloc = FastMalloc>
class Vector : private VectorBuffer<T, inlineCapacity, Malloc> {
The extra painful thing is that, contrary to what I originally thought, one
cannot declare Vector in Forward.h and then define it in Vector.h with the same
defaults twice! Ideally the compiler would just yell at a mismatch, but instead
it says error: template parameter redefines default argument (thanks clang,
that’s exactly what I’m trying to do, just tell me if you catch a mismatch and
ODR away otherwise).
Here’s what I propose:
Change the forward declaration in Forward.h to contain the default template
parameters (and forward-declare CrashOnOverflow).
Remove these default template parameters from Vector.h.
Include Forward.h in Vector.h.
Optionally, if the WebCritters think it useful, leave a comment just above the
Vector definition redirecting to Forward.h for defaults (or more fancy, use
size_t inlineCapacity /*=0*/ style like LLVM’s codebase does, and have a tool
that checks for consistency).
Optionally, try to fix C++20 so this isn’t A Thing anymore. Note that my hopes
are low because of modules (why fix it if modules will magically make this not
a thing).
Alternatively, I could just include Vector.h and be done with it.
Thoughts?
JF
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