pon., 23 sie 2021 o 18:32 Phil Endecott via Std-Proposals
<std-proposals_at_[hidden]> napisał(a):
>
> Dear Experts,
>
> I have been contemplating what the easiest current or future
> way to create a unique_ptr with a custom deleter function is.
>
> For example, libtiff has
>
> TIFF* TIFFOpen(args);
> void TIFFClose(TIFF*);
>
> I'd like to be able to write something like:
>
> auto tiffp = make_unique_with_deleter( TIFFOpen(fn), TIFFClose );
>
> Of course it can't be quite that simple. Fundamentally unique_ptr
> stores the deleter only in the type, which I think means the
> deleter function can only ever be a template parameter:
>
> auto tiffp = make_unique_with_deleter<TIFFClose>( TIFFOpen(fn) );
>
> I haven't quite worked out how to implement that yet; I can't
> avoid requiring the pointer type in the template list but I bet
> one of you experts knows how to avoid that:
>
> template <typename T, void(*DEL)(T*)>
> struct wrap_deleter
> {
> void operator()(T* p) const { DEL(p); }
> };
>
> template <typename T, void(*DEL)(T*)>
> auto make_unique_with_deleter(T* raw_ptr)
> {
> return std::unique_ptr<T, wrap_deleter<T,DEL>>(raw_ptr);
> }
>
> auto tiffp = make_unique_with_deleter<TIFF, TIFFClose>( TIFFOpen(fn) );
>
> So anyway:
>
> - Has anything like this been considered before?
> - Can anyone suggest how to avoid needing the type template parameter?
> - Have I missed an existing feature that can convert a function pointer
> value into a functor type, as my wrap_deleter does?
>

You can use `template<auto ptr>` and in helper type extract argument type.
This could even not need be function, simply any thing that is callable like:
```
std::invoke(ptr, p);
```

>
> Thanks, Phil.
>
>
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