diff options
Diffstat (limited to 'absl/container/flat_hash_set.h')
| -rw-r--r-- | absl/container/flat_hash_set.h | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/absl/container/flat_hash_set.h b/absl/container/flat_hash_set.h index 1be00195..5f72f954 100644 --- a/absl/container/flat_hash_set.h +++ b/absl/container/flat_hash_set.h @@ -60,7 +60,7 @@ struct FlatHashSetPolicy; // * Requires keys that are CopyConstructible // * Supports heterogeneous lookup, through `find()` and `insert()`, provided // that the set is provided a compatible heterogeneous hashing function and -// equality operator. +// equality operator. See below for details. // * Invalidates any references and pointers to elements within the table after // `rehash()` and when the table is moved. // * Contains a `capacity()` member function indicating the number of element @@ -78,6 +78,19 @@ struct FlatHashSetPolicy; // libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may // be randomized across dynamically loaded libraries. // +// To achieve heterogeneous lookup for custom types either `Hash` and `Eq` type +// parameters can be used or `T` should have public inner types +// `absl_container_hash` and (optionally) `absl_container_eq`. In either case, +// `typename Hash::is_transparent` and `typename Eq::is_transparent` should be +// well-formed. Both types are basically functors: +// * `Hash` should support `size_t operator()(U val) const` that returns a hash +// for the given `val`. +// * `Eq` should support `bool operator()(U lhs, V rhs) const` that returns true +// if `lhs` is equal to `rhs`. +// +// In most cases `T` needs only to provide the `absl_container_hash`. In this +// case `std::equal_to<void>` will be used instead of `eq` part. +// // NOTE: A `flat_hash_set` stores its keys directly inside its implementation // array to avoid memory indirection. Because a `flat_hash_set` is designed to // move data when rehashed, set keys will not retain pointer stability. If you |