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