#ifndef XBT_FUTURE_HPP
#define XBT_FUTURE_HPP
-#include <future>
+#include <cstddef>
+
#include <utility>
#include <exception>
namespace simgrid {
namespace xbt {
+/** A value or an exception
+ *
+ * The API is similar to the one of future and promise.
+ **/
+template<class T>
+class Result {
+ enum class ResultStatus {
+ invalid,
+ value,
+ exception,
+ };
+public:
+ Result() {}
+ ~Result() { this->reset(); }
+
+ // Copy (if T is copyable) and move:
+ Result(Result const& that)
+ {
+ (*this) = that;
+ }
+ Result& operator=(Result const& that)
+ {
+ this->reset();
+ switch (that.status_) {
+ case ResultStatus::invalid:
+ break;
+ case ResultStatus::valid:
+ new (&value_) T(that.value);
+ break;
+ case ResultStatus::exception:
+ new (&exception_) T(that.exception);
+ break;
+ }
+ return *this;
+ }
+ Result(Result&& that)
+ {
+ *this = std::move(that);
+ }
+ Result& operator=(Result&& that)
+ {
+ this->reset();
+ switch (that.status_) {
+ case ResultStatus::invalid:
+ break;
+ case ResultStatus::valid:
+ new (&value_) T(std::move(that.value));
+ that.value.~T();
+ break;
+ case ResultStatus::exception:
+ new (&exception_) T(std::move(that.exception));
+ that.exception.~exception_ptr();
+ break;
+ }
+ that.status_ = ResultStatus::invalid;
+ return *this;
+ }
+
+ bool is_valid()
+ {
+ return status_ != ResultStatus::invalid;
+ }
+ void reset()
+ {
+ switch(status_) {
+ case ResultStatus::invalid:
+ break;
+ case ResultStatus::value:
+ value_.~T();
+ break;
+ case ResultStatus::exception:
+ exception_.~exception_ptr();
+ break;
+ }
+ status_ = ResultStatus::invalid;
+ }
+ void set_exception(std::exception_ptr e)
+ {
+ this->reset();
+ new (&exception_) std::exception_ptr(std::move(e));
+ status_ = ResultStatus::exception;
+ }
+ void set_value(T&& value)
+ {
+ this->reset();
+ new (&value_) T(std::move(value));
+ status_ = ResultStatus::value;
+ }
+ void set_value(T const& value)
+ {
+ this->reset();
+ new (&value_) T(value);
+ status_ = ResultStatus::value;
+ }
+
+ /** Extract the value from the future
+ *
+ * After this the value is invalid.
+ **/
+ T get()
+ {
+ switch(status_) {
+ case ResultStatus::invalid:
+ default:
+ throw std::logic_error("Invalid result");
+ case ResultStatus::value: {
+ T value = std::move(value_);
+ value_.~T();
+ status_ = ResultStatus::invalid;
+ return std::move(value);
+ }
+ case ResultStatus::exception: {
+ std::exception_ptr exception = std::move(exception_);
+ exception_.~exception_ptr();
+ status_ = ResultStatus::invalid;
+ std::rethrow_exception(std::move(exception));
+ break;
+ }
+ }
+ }
+private:
+ ResultStatus status_ = ResultStatus::invalid;
+ union {
+ T value_;
+ std::exception_ptr exception_;
+ };
+};
+
+template<>
+class Result<void> : public Result<nullptr_t>
+{
+public:
+ void set_value()
+ {
+ Result<std::nullptr_t>::set_value(nullptr);
+ }
+ void get()
+ {
+ Result<nullptr_t>::get();
+ }
+};
+
+template<class T>
+class Result<T&> : public Result<std::reference_wrapper<T>>
+{
+public:
+ void set_value(T& value)
+ {
+ Result<std::reference_wrapper<T>>::set_value(std::ref(value));
+ }
+ T& get()
+ {
+ return Result<std::reference_wrapper<T>>::get();
+ }
+};
+
/** Fulfill a promise by executing a given code */
template<class R, class F>
-void fulfillPromise(std::promise<R>& promise, F code)
+auto fulfillPromise(R& promise, F&& code)
+-> decltype(promise.set_value(code()))
{
try {
promise.set_value(code());
* This is a special version for `std::promise<void>` because the default
* version does not compile in this case.
*/
-template<class F>
-void fulfillPromise(std::promise<void>& promise, F code)
+template<class P, class F>
+auto fulfillPromise(P& promise, F&& code)
+-> decltype(promise.set_value())
{
try {
(code)();
