On Fri, 26 Mar 2021 at 21:32, Barry Revzin via SG7 <sg7_at_[hidden]> wrote:
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> On Fri, Mar 26, 2021 at 2:00 PM David Rector via SG7 <sg7_at_[hidden]> wrote:
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>> Attached is a new paper addressing how the P2237/P2230 facilities might be expanded to be able handle the `Sum<T,U>` example discussed awhile back, and more generally subsume the capabilities of the "string-injection" approach, while avoiding its drawbacks.
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> Hi David,
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> I didn't understand the Sum<T, U> example before and I still don't. There's not really a description of it in the paper, just a lot of code. What problem is it demonstrating?

I don't understand the lack of understanding. It's basically

For two types T and U
 - generate a product-type wrapper X that
   * for every member function $foo appearing in both T and U, has a
member function X::$foo that returns the sum of the results of T::$foo
and U::$foo
   * otherwise, for any member function $bar appearing in just one of
T and U, has a member function X::$bar that returns the result of
either T::$bar
     or U::$bar depending on which one is present

It's just an example of a wrapper like that, a particular kind of
mediator, where the API is the union of the APIs of the mediated
types.