cor3ntin bc8b19c757 [Clang] Introduce a trait to determine the structure binding size (#131515) ...

Introduce a trait to determine the number of bindings that would be
produced by

```cpp

   auto [...p] = expr;

```

This is necessary to implement P2300
(https://eel.is/c++draft/exec#snd.concepts-5), but can also be used to
implement a general get<N> function that supports aggregates

`__builtin_structured_binding_size` is a unary type trait that evaluates
to the number of bindings in a decomposition

If the argument cannot be decomposed, a sfinae-friendly error is
produced.

A type is considered a valid tuple if `std::tuple_size_v<T>` is a valid
expression, even if there is no valid `std::tuple_element`
specialization or suitable `get` function for that type.


Fixes #46049

2025-03-18 20:50:56 +01:00

2.2 KiB

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