From: Adam Simpkins <simpkins@fb.com>
Date: Thu, 22 Jun 2017 20:39:56 +0000 (-0700)
Subject: allow passing function pointers to Future::onError()
X-Git-Tag: v2017.06.26.00~15
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=folly.git;a=commitdiff_plain;h=49f2f8b170dfee4871a84c57d6e149623126a2d3;ds=sidebyside

allow passing function pointers to Future::onError()

Summary:
Add appropriate specializations for detail::Extract() so that you can pass a
plain function pointer to `onError()`.  Previously the code only worked with
member function pointers and functor-style objects.

Reviewed By: yfeldblum, wez

Differential Revision: D5286773

fbshipit-source-id: 67b44d1d7573eb1da501475045fd24ad4ab1c074
---

diff --git a/folly/futures/Future-pre.h b/folly/futures/Future-pre.h
index e3f5021e..bcae5b08 100644
--- a/folly/futures/Future-pre.h
+++ b/folly/futures/Future-pre.h
@@ -119,6 +119,22 @@ struct Extract<R(Class::*)(Args...)> {
   typedef typename ArgType<Args...>::FirstArg FirstArg;
 };
 
+template <typename R, typename... Args>
+struct Extract<R (*)(Args...)> {
+  typedef isFuture<R> ReturnsFuture;
+  typedef Future<typename ReturnsFuture::Inner> Return;
+  typedef typename ReturnsFuture::Inner RawReturn;
+  typedef typename ArgType<Args...>::FirstArg FirstArg;
+};
+
+template <typename R, typename... Args>
+struct Extract<R (&)(Args...)> {
+  typedef isFuture<R> ReturnsFuture;
+  typedef Future<typename ReturnsFuture::Inner> Return;
+  typedef typename ReturnsFuture::Inner RawReturn;
+  typedef typename ArgType<Args...>::FirstArg FirstArg;
+};
+
 // gcc-4.8 refuses to capture a function reference in a lambda. This can be
 // mitigated by casting them to function pointer types first. The following
 // helper is used in Future.h to achieve that where necessary.
diff --git a/folly/futures/test/FutureTest.cpp b/folly/futures/test/FutureTest.cpp
index 3bfb8e33..3322d2f4 100644
--- a/folly/futures/test/FutureTest.cpp
+++ b/folly/futures/test/FutureTest.cpp
@@ -76,6 +76,15 @@ TEST(Future, makeFutureWithUnit) {
   EXPECT_EQ(1, count);
 }
 
+namespace {
+Future<int> onErrorHelperEggs(const eggs_t&) {
+  return makeFuture(10);
+}
+Future<int> onErrorHelperGeneric(const std::exception&) {
+  return makeFuture(20);
+}
+}
+
 TEST(Future, onError) {
   bool theFlag = false;
   auto flag = [&]{ theFlag = true; };
@@ -191,6 +200,28 @@ TEST(Future, onError) {
     EXPECT_NO_THROW(f.value());
   }
 
+  // Function pointer
+  {
+    auto f = makeFuture()
+                 .then([]() -> int { throw eggs; })
+                 .onError(onErrorHelperEggs)
+                 .onError(onErrorHelperGeneric);
+    EXPECT_EQ(10, f.value());
+  }
+  {
+    auto f = makeFuture()
+                 .then([]() -> int { throw std::runtime_error("test"); })
+                 .onError(onErrorHelperEggs)
+                 .onError(onErrorHelperGeneric);
+    EXPECT_EQ(20, f.value());
+  }
+  {
+    auto f = makeFuture()
+                 .then([]() -> int { throw std::runtime_error("test"); })
+                 .onError(onErrorHelperEggs);
+    EXPECT_THROW(f.value(), std::runtime_error);
+  }
+
   // No throw
   {
     auto f = makeFuture()