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//
// Copyright 2013 Francisco Jerez
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
// OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.
//
#ifndef CLOVER_UTIL_LAZY_HPP
#define CLOVER_UTIL_LAZY_HPP
#include <type_traits>
#include <stdexcept>
#include <memory>
namespace clover {
namespace detail {
template<typename T>
class basic_lazy {
public:
virtual
~basic_lazy() {
}
virtual basic_lazy *
clone() const = 0;
virtual
operator T() const = 0;
};
template<typename T, typename F>
class deferred_lazy : public basic_lazy<T> {
public:
template<typename G>
deferred_lazy(G &&f) : f(new F(std::forward<G>(f))) {
}
virtual basic_lazy<T> *
clone() const {
return new deferred_lazy(*this);
}
operator T() const {
if (f) {
x = (*f)();
f = {};
}
return x;
}
private:
mutable std::shared_ptr<F> f;
mutable T x;
};
template<typename T>
class strict_lazy : public basic_lazy<T> {
public:
template<typename S>
strict_lazy(S &&x) : x(std::forward<S>(x)) {
}
virtual basic_lazy<T> *
clone() const {
return new strict_lazy(*this);
}
operator T() const {
return x;
}
private:
T x;
};
}
///
/// Object that represents a value of type \a T that is calculated
/// lazily as soon as it is required.
///
template<typename T>
class lazy {
public:
class undefined_error : std::logic_error {
public:
undefined_error() : std::logic_error("") {
}
};
///
/// Initialize to some fixed value \a x which isn't calculated
/// lazily.
///
lazy(T x) : obj(new detail::strict_lazy<T>(x)) {
}
///
/// Initialize by providing a functor \a f that will calculate
/// the value on-demand.
///
template<typename F>
lazy(F &&f) : obj(new detail::deferred_lazy<
T, typename std::remove_reference<F>::type
>(std::forward<F>(f))) {
}
///
/// Initialize to undefined.
///
lazy() : lazy([]() {
throw undefined_error();
return T();
}) {
}
lazy(const lazy &other) : obj(obj->clone()) {
}
lazy(lazy &&other) : obj(NULL) {
std::swap(obj, other.obj);
}
~lazy() {
delete obj;
}
lazy &
operator=(lazy other) {
std::swap(obj, other.obj);
return *this;
}
///
/// Evaluate the value.
///
operator T() const {
return *obj;
}
private:
detail::basic_lazy<T> *obj;
};
}
#endif
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