/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2016 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#pragma once
#include <folly/futures/Future.h>
+#include <folly/Portability.h>
namespace folly {
/** Make a completed void Future. */
Future<Unit> makeFuture();
-/** Make a completed Future by executing a function. If the function throws
- we capture the exception, otherwise we capture the result. */
+/**
+ Make a Future by executing a function.
+
+ If the function returns a value of type T, makeFutureWith
+ returns a completed Future<T>, capturing the value returned
+ by the function.
+
+ If the function returns a Future<T> already, makeFutureWith
+ returns just that.
+
+ Either way, if the function throws, a failed Future is
+ returned that captures the exception.
+
+ Calling makeFutureWith(func) is equivalent to calling
+ makeFuture().then(func).
+*/
+
+// makeFutureWith(Future<T>()) -> Future<T>
+template <class F>
+typename std::enable_if<isFuture<typename std::result_of<F()>::type>::value,
+ typename std::result_of<F()>::type>::type
+makeFutureWith(F&& func);
+
+// makeFutureWith(T()) -> Future<T>
+// makeFutureWith(void()) -> Future<Unit>
template <class F>
-auto makeFutureWith(F&& func)
- -> Future<typename Unit::Lift<decltype(func())>::type>;
+typename std::enable_if<
+ !(isFuture<typename std::result_of<F()>::type>::value),
+ Future<typename Unit::Lift<typename std::result_of<F()>::type>::type>>::type
+makeFutureWith(F&& func);
/// Make a failed Future from an exception_ptr.
/// Because the Future's type cannot be inferred you have to specify it, e.g.
///
/// auto f = makeFuture<string>(std::current_exception());
template <class T>
-DEPRECATED Future<T> makeFuture(std::exception_ptr const& e);
+FOLLY_DEPRECATED("use makeFuture(exception_wrapper)")
+Future<T> makeFuture(std::exception_ptr const& e);
/// Make a failed Future from an exception_wrapper.
template <class T>
/// This is semantically equivalent to via(executor).then(func), but
/// easier to read and slightly more efficient.
template <class Func>
-auto via(Executor*, Func func)
+auto via(Executor*, Func&& func)
-> Future<typename isFuture<decltype(func())>::Inner>;
/** When all the input Futures complete, the returned Future will complete.
Duration backoff_min,
Duration backoff_max,
double jitter_param,
- URNG rng,
+ URNG&& rng,
Policy&& p);
inline