diff options
Diffstat (limited to 'absl/container/node_hash_map.h')
| -rw-r--r-- | absl/container/node_hash_map.h | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/absl/container/node_hash_map.h b/absl/container/node_hash_map.h index 72e78958..cb41543c 100644 --- a/absl/container/node_hash_map.h +++ b/absl/container/node_hash_map.h @@ -67,7 +67,7 @@ class NodeHashMapPolicy; // // * Supports heterogeneous lookup, through `find()`, `operator[]()` and // `insert()`, provided that the map is provided a compatible heterogeneous -// hashing function and equality operator. +// hashing function and equality operator. See below for details. // * Contains a `capacity()` member function indicating the number of element // slots (open, deleted, and empty) within the hash map. // * Returns `void` from the `erase(iterator)` overload. @@ -83,6 +83,19 @@ class NodeHashMapPolicy; // 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. +// // Example: // // // Create a node hash map of three strings (that map to strings) |