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99 lines
2.8 KiB
C++
99 lines
2.8 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef EXECUTABLE_SEMANTICS_INTERPRETER_DICTIONARY_H_
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#define EXECUTABLE_SEMANTICS_INTERPRETER_DICTIONARY_H_
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#include <iterator>
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#include <optional>
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#include "executable_semantics/common/arena.h"
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namespace Carbon {
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// A persistent dictionary with a simple implementation.
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// Copying the dictionary is O(1) time.
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template <class K, class V>
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class Dictionary {
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public:
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struct Node {
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using ValueType = std::pair<K, V>;
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Node(ValueType e, std::optional<Ptr<Node>> n) : curr(e), next(n) {}
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const ValueType curr;
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const std::optional<Ptr<Node>> next;
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// Node cells are part of a "persistent data structure" and are thus
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// immutable.
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Node& operator=(const Node&) = delete;
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Node& operator=(Node&&) = delete;
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};
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// A forward iterator over elements of a `Node` list.
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struct Iterator {
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using value_type = typename Node::ValueType;
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using difference_type = std::ptrdiff_t;
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using pointer = const value_type*;
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using reference = const value_type&;
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using iterator_category = std::forward_iterator_tag;
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Iterator(std::optional<Ptr<Node>> x) : p(x) {}
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Iterator(const Iterator& iter) : p(iter.p) {}
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Iterator& operator++() {
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p = (*p)->next;
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return *this;
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}
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Iterator operator++(int) {
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Iterator tmp(*this);
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operator++();
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return tmp;
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}
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bool operator==(const Iterator& rhs) const { return p == rhs.p; }
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bool operator!=(const Iterator& rhs) const { return p != rhs.p; }
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const value_type& operator*() { return (*p)->curr; }
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const value_type* operator->() { return &(*p)->curr; }
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private:
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std::optional<Ptr<Node>> p;
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};
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// Create an empty dictionary.
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Dictionary() {}
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// Return the value associated with the given key.
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// Time complexity: O(n) where n is the number of times
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// any value has been set across all keys.
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auto Get(const K& key) -> std::optional<V> {
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for (auto kv : *this) {
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if (kv.first == key) {
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return kv.second;
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}
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}
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return std::nullopt;
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}
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// Associate the value v with key k in the dictionary.
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// Time complexity: O(1).
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auto Set(const K& k, const V& v) -> void {
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head = global_arena->New<Node>(std::make_pair(k, v), head);
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}
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bool IsEmpty() { return !head; }
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// The position of the first element of the dictionary
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// or `end()` if the dictionary is empty.
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auto begin() const -> Iterator { return Iterator(head); }
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// The position one past that of the last element.
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auto end() const -> Iterator { return Iterator(std::nullopt); }
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private:
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std::optional<Ptr<Node>> head;
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};
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} // namespace Carbon
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#endif // EXECUTABLE_SEMANTICS_INTERPRETER_DICTIONARY_H_
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