constant_cell.hpp

/*
 * live_cells_cpp
 * Copyright (C) 2024  Alexander Gutev <alex.gutev@gmail.com>
 *
 * 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
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied.  See the License for the specific language governing
 * permissions and limitations under the License.
 */
 
#ifndef LIVE_CELLS_CONSTANT_CELL_HPP
#define LIVE_CELLS_CONSTANT_CELL_HPP
 
#include <functional>
#include <memory>
 
#include "observable.hpp"
 
namespace live_cells {
 
    template <typename T>
    struct constant_key : key {
        const T value;
 
        constant_key(T value) : value(value) {}
 
        bool eq(const key &k) const noexcept override {
            auto *ptr = dynamic_cast<const constant_key*>(&k);
 
            return ptr != nullptr && value == ptr->value;
        }
 
        std::size_t hash() const noexcept override {
            return std::hash<T>{}(value);
        }
    };
 
    template <typename T>
    class constant_cell {
    public:
        typedef T value_type;
 
        constant_cell(const T &value) : m_value(value) {}
 
        key_ref key() const {
            return key_ref::create<constant_key<T>>(m_value);
        }
 
        T value() const {
            return m_value;
        }
 
        void add_observer(observer::ref) const {
            // Do nothing
        }
 
        void remove_observer(observer::ref) const {
            // Do nothing
        }
 
        T operator()() const {
            // No need to track a constant cell
            return m_value;
        }
 
    private:
        const T m_value;
 
    };
 
    template <typename T>
    constant_cell<T> value(const T &value) {
        return constant_cell<T>(value);
    }
 
    template <typename T>
    concept CellOrValue = Cell<T> || std::constructible_from<constant_cell<T>, T>;
 
    auto ensure_cell(const Cell auto &thing) {
        return thing;
    }
 
    template <typename T>
    auto ensure_cell(const T& thing) {
        return constant_cell<T>(thing);
    }
 
}  // live_cells
 
#endif /* LIVE_CELLS_CONSTANT_CELL_HPP */