Re: [boost] [proposal] OpenMethod library

11 Mar 2025

      ...
Doesn't show the overloading part, but that's OK.
...
Quick question: Given the ability to return different (necessarily related?)
types from the same open-method, can we say BOM allows co-variant return type?
Like virtual methods / polymorphism allows, just more flexible that plain
pointers?
Yes. And in that case, the return type can act as a tie-breaker, as described in
N2216.

Here is `transpose` with `const` and covariant return types:

    BOOST_OPENMETHOD(
        transpose, (shared_virtual_ptr<const Matrix>),
        shared_virtual_ptr<const Matrix>);

    BOOST_OPENMETHOD_OVERRIDE(
        transpose, (shared_virtual_ptr<const OrdinaryMatrix>),
        shared_virtual_ptr<const OrdinaryMatrix>) {
        return make_shared_virtual<OrdinaryMatrix>();
    }

    BOOST_OPENMETHOD_OVERRIDE(
        transpose, (shared_virtual_ptr<const SymmetricMatrix> m),
        shared_virtual_ptr<const SymmetricMatrix>) {
        return m;
    }

You can call a specific overrider like so:

    auto u = BOOST_OPENMETHOD_OVERRIDERS(
        transpose)::fn(m);
    static_assert(
        std::is_same_v);

(Compiler Explorer: https://godbolt.org/z/ndKaKWPzd)

J-L

On Tue, Mar 11, 2025 at 4:59 AM Dominique Devienne  wrote:
...
On Mon, Mar 10, 2025 at 9:45 PM Jean-Louis Leroy via Boost
 wrote:
...
...
...
[...] handling of const-ness
`const` is supported.
Doesn't show the overloading part, but that's OK.
Quick question: Given the ability to return different (necessarily
related?) types
from the same open-method, can we say BOM allows co-variant return type?
Like virtual methods / polymorphism allows, just more flexible that
plain pointers?
Thanks, --DD