optional.hpp

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/*
 * Copyright 2017, alex at staticlibs.net
 *
 * 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.
 */

/* 
 * File:   optional.hpp
 * Author: alex
 *
 * Created on February 4, 2017, 7:40 PM
 */

#ifndef STATICLIB_SUPPORT_OPTIONAL_HPP
#define STATICLIB_SUPPORT_OPTIONAL_HPP

#include <type_traits>

#include "staticlib/config.hpp"

#include "staticlib/support/exception.hpp"

namespace staticlib {
namespace support {

class bad_optional_access_exception : public exception {
public:
    bad_optional_access_exception() :
    exception("Invalid attempt to access non-initialized value of 'optional' object") { }
};

template<typename T>
class optional {
    typename std::aligned_storage<sizeof(T), std::alignment_of<T>::value>::type value_space;
    
    T* value_ptr = nullptr;
    
public:
    
    optional() { }
    
    explicit optional(T&& value) :
    value_ptr(new (std::addressof(value_space)) T(std::move(value))) { }
    
    optional(const optional&) = delete;
    
    optional& operator=(const optional&) = delete;
    
    optional(optional&& other) STATICLIB_NOEXCEPT {
        if(other.has_value())  {
            value_ptr = new (std::addressof(value_space)) T(std::move(other.value()));
            other.reset();
        }
    }
    
    optional& operator=(optional&& other) STATICLIB_NOEXCEPT {
        reset();
        if (other.has_value()) {
            value_ptr = new (std::addressof(value_space)) T(std::move(other.value()));
            other.reset();
        }
        return *this;
    }
    
    ~optional() STATICLIB_NOEXCEPT {
        if (has_value()) {
            value_ptr->~T();
        }
    }
    
    explicit operator bool() const {
        return has_value();
    }
    
    bool has_value() const {
        return nullptr != value_ptr;
    }

    T& value() {
        if(has_value()) {
            return *value_ptr;
        } else {
            throw bad_optional_access_exception();
        }
    }

    const T& value() const {
        if (has_value()) {
            return *value_ptr;
        } else {
            throw bad_optional_access_exception();
        }
    }

    T value_or(T&& default_value) const {
        if (has_value()) {
            // copy constructor called
            return *value_ptr;
        }
        return std::move(default_value);
    }

    T value_or(T&& default_value) {
        if (has_value()) {
            return std::move(*value_ptr);
        }
        return std::move(default_value);
    }
            
    void reset() {
        if (has_value()) {
            value_ptr->~T();
        }
        value_ptr = nullptr;
    }
    
};

template<typename T>
optional<T> make_optional(T&& value) {
    return optional<T>(std::move(value));
}

} // namespace
}


#endif /* STATICLIB_SUPPORT_OPTIONAL_HPP */