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// Copyright 2022 The Tint Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include <functional>
#include <unordered_set>
#include <utility>
#include "src/tint/utils/block_allocator.h"
namespace tint::utils {
/// UniqueAllocator is used to allocate unique instances of the template type
/// `T`.
template <typename T, typename HASH = std::hash<T>, typename EQUAL = std::equal_to<T>>
class UniqueAllocator {
/// @param args the arguments used to construct the object.
/// @return a pointer to an instance of `T` with the provided arguments.
/// If an existing instance of `T` has been constructed, then the same
/// pointer is returned.
template <typename TYPE = T, typename... ARGS>
TYPE* Get(ARGS&&... args) {
// Create a temporary T instance on the stack so that we can hash it, and
// use it for equality lookup for the std::unordered_set. If the item is not
// found in the set, then we create the persisted instance with the
// allocator.
TYPE key{args...};
auto hash = Hasher{}(key);
auto it = items.find(Entry{hash, &key});
if (it != items.end()) {
return static_cast<TYPE*>(it->ptr);
auto* ptr = allocator.template Create<TYPE>(std::forward<ARGS>(args)...);
items.emplace_hint(it, Entry{hash, ptr});
return ptr;
/// The hash function
using Hasher = HASH;
/// The equality function
using Equality = EQUAL;
/// Entry is used as the entry to the unordered_set
struct Entry {
/// The pre-calculated hash of the entry
size_t hash;
/// Tge pointer to the unique object
T* ptr;
/// Comparator is the hashing and equality function used by the unordered_set
struct Comparator {
/// Hashing function
/// @param e the entry
/// @returns the hash of the entry
size_t operator()(Entry e) const { return e.hash; }
/// Equality function
/// @param a the first entry to compare
/// @param b the second entry to compare
/// @returns true if the two entries are equal
bool operator()(Entry a, Entry b) const { return EQUAL{}(*a.ptr, *b.ptr); }
/// The block allocator used to allocate the unique objects
BlockAllocator<T> allocator;
/// The unordered_set of unique item entries
std::unordered_set<Entry, Comparator, Comparator> items;
} // namespace tint::utils