diff options
Diffstat (limited to 'source/blender/blenlib/BLI_hash.hh')
| -rw-r--r-- | source/blender/blenlib/BLI_hash.hh | 22 |
1 files changed, 19 insertions, 3 deletions
diff --git a/source/blender/blenlib/BLI_hash.hh b/source/blender/blenlib/BLI_hash.hh index 4022c2baa1f..fbed321534c 100644 --- a/source/blender/blenlib/BLI_hash.hh +++ b/source/blender/blenlib/BLI_hash.hh @@ -85,9 +85,12 @@ namespace blender { /** - * If there is no other specialization of #DefaultHash for a given type, try to call `hash()` on - * the value. If there is no such method, this will result in a compiler error. Usually that means - * that you have to implement a hash function using one of three strategies listed above. + * If there is no other specialization of #DefaultHash for a given type, look for a hash function + * on the type itself. Implementing a `hash()` method on a type is often significantly easier than + * specializing #DefaultHash. + * + * To support heterogeneous lookup, a type can also implement a static `hash_as(const OtherType &)` + * function. * * In the case of an enum type, the default hash is just to cast the enum value to an integer. */ @@ -95,12 +98,25 @@ template<typename T> struct DefaultHash { uint64_t operator()(const T &value) const { if constexpr (std::is_enum_v<T>) { + /* For enums use the value as hash directly. */ return (uint64_t)value; } else { + /* Try to call the `hash()` function on the value. */ + /* If this results in a compiler error, no hash function for the type has been found. */ return value.hash(); } } + + template<typename U> uint64_t operator()(const U &value) const + { + /* Try calling the static `T::hash_as(value)` function with the given value. The returned hash + * should be "compatible" with `T::hash()`. Usually that means that if `value` is converted to + * `T` its hash does not change. */ + /* If this results in a compiler error, no hash function for the heterogeneous lookup has been + * found. */ + return T::hash_as(value); + } }; /** |