to_shared_ptr.

Summary: [Folly] to_shared_ptr.

So you can write this:

    auto sptr = to_shared_ptr(getSomethingUnique<T>());

Instead of this:

    auto sptr = shared_ptr<T>(getSomethingUnique<T>());

Useful when `T` is long, such as `T = foobar::cpp2::FooBarServiceAsyncClient`.

Reviewed By: @meyering

Differential Revision: D2193572

folly/Memory.h

@@ -56,6 +56,29 @@ typename std::enable_if<
   std::extent<T>::value != 0, std::unique_ptr<T, Dp>>::type
 make_unique(Args&&...) = delete;
 
+/**
+ *  to_shared_ptr
+ *
+ *  Convert unique_ptr to shared_ptr without specifying the template type
+ *  parameter and letting the compiler deduce it.
+ *
+ *  So you can write this:
+ *
+ *      auto sptr = to_shared_ptr(getSomethingUnique<T>());
+ *
+ *  Instead of this:
+ *
+ *      auto sptr = shared_ptr<T>(getSomethingUnique<T>());
+ *
+ *  Useful when `T` is long, such as:
+ *
+ *      using T = foobar::cpp2::FooBarServiceAsyncClient;
+ */
+template <typename T>
+std::shared_ptr<T> to_shared_ptr(std::unique_ptr<T>&& ptr) {
+  return std::shared_ptr<T>(std::move(ptr));
+}
+
 /**
  * A SimpleAllocator must provide two methods:
  *

folly/test/MemoryTest.cpp

@@ -25,6 +25,13 @@
 
 using namespace folly;
 
+TEST(shared_ptr, example) {
+  auto uptr = make_unique<std::string>("hello");
+  auto sptr = to_shared_ptr(std::move(uptr));
+  EXPECT_EQ(nullptr, uptr);
+  EXPECT_EQ("hello", *sptr);
+}
+
 template <std::size_t> struct T {};
 template <std::size_t> struct S {};
 template <std::size_t> struct P {};