tree b033c8576ce026503830bbdf1a57603fa8cc4a24
parent e3826891272d239bb2836bf6a2167b44d057d8be
author Vitaly Goldshteyn <goldvitaly@google.com> 1788375583 -0700
committer Copybara-Service <copybara-worker@google.com> 1788375623 -0700

Introduce absl::TransparentHash for transparent hashing of multiple types.

absl::TransparentHash<Ts...> is a hash functor that can hash any of the types Ts... It is marked as transparent (is_transparent = void). This allows containers like absl::flat_hash_map to use a single hash functor for lookups with different but comparable types (e.g., std::string and absl::string_view).

Added a test case in absl/hash/hash_test.cc using Name and NameView to demonstrate and test absl::TransparentHash with a custom transparent equality functor.

```
name                 cpu/op       cpu/op     vs base
BM_TransparentFind   2.620n ± 1%   2.413n ± 1%  -7.90% (p=0.002 n=6)

name                 time/op       time/op     vs base
BM_TransparentFind   2.625n ± 1%   2.418n ± 1%  -7.87% (p=0.002 n=6)

name                 INSTRUCTIONS/op  INSTRUCTIONS/op  vs base
BM_TransparentFind    45.07 ± 0%        42.07 ± 0%  -6.67% (p=0.002 n=6)

name                 CYCLES/op   CYCLES/op   vs base
BM_TransparentFind    9.229 ± 0%   8.492 ± 0%  -7.98% (p=0.002 n=6)
```

PiperOrigin-RevId: 975251791
Change-Id: I7400e103167d707366f0be82dce627ab478959dd