[llvm-dev] RFC: Towards unified semantic for casts

David Blaikie via llvm-dev llvm-dev at lists.llvm.org
Tue Jan 23 08:57:41 PST 2018

Looks pretty reasonable to me - with test cases. (not sure if
dereferenced_type should be defined for a type that's not dereferenceable,

On Tue, Jan 23, 2018 at 7:02 AM Dmitriy Borisenkov via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi everyone,
> I have an idea that should allow reducing code duplication in Casting.h
> while making llvm::isa, llvm::cast, llvm::dyn_cast, etc more generic. Since
> we added unique pointers support for these template functions (see
> ab480f45cd23c08cb9aa3f427aad072df249135f) I propose to generalize their
> semantics to deal with any pointer-like type (i.e. dereferenceable and
> implicitly convertible to bool) so that:
>    - for each fancy_pointer<T> t: isa<G>(t) returns true iff current
>    implementation of isa<G>(nonfancy_t) returns true where
>    decltype(nonfancy_t) is T*
>    - all old cast operations should return a raw pointer of type typename
>    std::pointer_traits<fancy_pointer<T>>::element_type * and do not perform
>    ownership transfer.
>    - move_[dyn_]cast should do what unique_dyn_cast is currently doing in
>    a more generic manner: it moves to an object of type typename
>    std::pointer_traits<fancy_pointer<T>>::rebind<G>
> N.B. std::pointer_traits is a conception that I use to explain the
> behaviour - not necessary the way I plan to implement it.
> An example implementation of the proposal for llvm::isa :
> https://reviews.llvm.org/D42027
> --
> Kind regards, Dmitry
> _______________________________________________
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> llvm-dev at lists.llvm.org
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