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by signa11 326 days ago
> I think there's room for a `C+` language, by which I mean C+templates and not C+classes - perhaps with an ABI which is a subset of the C++ ABI but superset of the C ABI.

indeed, i have spoken to a lot of my colleagues about just that. if overloading is not allowed, perhaps there is still some hope for a backwards compatible abi ?
2 comments
sparkie 326 days ago
I don't think we can get away with just using the C ABI - or even if we did, we would need a standardized name-mangling scheme, and then any language which consumes the ABI would need to be aware of this name-mangling scheme, so it would effectively be a new ABI.

We might be able to make this ABI compatible with C if no templates are used, which wouldn't cause breaking changes - but for other compilers to be able to use templates they would need to opt-in to the new scheme. For that we'd probably want to augment libffi to include completely new functions for dealing with templates. Eg, we'd have an ffi_template_type, and an ffi_prep_template for which we supply its type arguments - then an ffi_prep_templated_cif for calls which use templates, and so forth. It would basically be a new API - but probably still more practical than trying to support the C++ ABI.

Another issue is that if we compile some library with templates and expose them in the ABI, we need some way to instantiate the template with new types which were not present when the library was compiled. There's no trivial solution to this. We'd really need to JIT-compile the templates.

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signa11 326 days ago
> ... we would need a standardized name-mangling scheme, ...

may you please elaborate on _why_ you think this is needed ?

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sparkie 326 days ago
If the templates are monomorphized, each instantiation of a templated function will have a different address. To acquire the address of any given instantiation we need a symbol in the object file.
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uecker 326 days ago
What isn't clear to me why one would ever want monomorphization in the first place.
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aw1621107 325 days ago
Not ever wanting monomorphization seems like a bit of a strong claim to me. Why do you take that position?
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uecker 324 days ago
I was asking the question why one would ever want it.
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signa11 326 days ago
exactly !
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cherryteastain 326 days ago
How can you have templates without name mangling and overloads?
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