identity

Summary: [Folly] `identity`, an initialized function object matching `Identity`, which is renamed `identity_fn`.

Reviewed By: markisaa, lewissbaker

Differential Revision: D21265889

fbshipit-source-id: 5cc9f2e624da9a4acd0f65985ff10a4dd306efdc

folly/Utility.h

@@ -247,25 +247,27 @@ struct transparent : T {
  * Example:
  *
  *   int i = 42;
- *   int &j = Identity()(i);
+ *   int &j = identity(i);
  *   assert(&i == &j);
  *
- * Warning: passing a prvalue through Identity turns it into an xvalue,
+ * Warning: passing a prvalue through identity turns it into an xvalue,
  * which can effect whether lifetime extension occurs or not. For instance:
  *
  *   auto&& x = std::make_unique<int>(42);
  *   cout << *x ; // OK, x refers to a valid unique_ptr.
  *
- *   auto&& y = Identity()(std::make_unique<int>(42));
+ *   auto&& y = identity(std::make_unique<int>(42));
  *   cout << *y ; // ERROR: y did not lifetime-extend the unique_ptr. It
  *                // is no longer valid
  */
-struct Identity {
+struct identity_fn {
   template <class T>
   constexpr T&& operator()(T&& x) const noexcept {
     return static_cast<T&&>(x);
   }
 };
+using Identity = identity_fn;
+FOLLY_INLINE_VARIABLE constexpr identity_fn identity;
 
 namespace moveonly_ { // Protection from unintended ADL.
 

folly/ssl/test/OpenSSLCertUtilsTest.cpp

@@ -171,17 +171,17 @@ static void validateTestCertBundle(
     const std::vector<folly::ssl::X509UniquePtr>& certs) {
   EXPECT_EQ(certs.size(), 3);
   for (auto i : folly::enumerate(certs)) {
-    auto identity = folly::ssl::OpenSSLCertUtils::getCommonName(**i);
-    EXPECT_TRUE(identity);
-    EXPECT_EQ(*identity, folly::sformat("test cert {}", i.index + 1));
+    auto cn = folly::ssl::OpenSSLCertUtils::getCommonName(**i);
+    EXPECT_TRUE(cn);
+    EXPECT_EQ(*cn, folly::sformat("test cert {}", i.index + 1));
   }
 }
 
 // Validate parsed cert from kTestCertWithSan.
 static void validateTestCertWithSAN(X509* x509) {
   ASSERT_NE(nullptr, x509);
-  auto identity = folly::ssl::OpenSSLCertUtils::getCommonName(*x509);
-  EXPECT_EQ("127.0.0.1", identity.value());
+  auto cn = folly::ssl::OpenSSLCertUtils::getCommonName(*x509);
+  EXPECT_EQ("127.0.0.1", cn.value());
   auto altNames = folly::ssl::OpenSSLCertUtils::getSubjectAltNames(*x509);
   EXPECT_EQ(2, altNames.size());
   EXPECT_EQ("anotherexample.com", altNames[0]);
@@ -191,8 +191,8 @@ static void validateTestCertWithSAN(X509* x509) {
 TEST_P(OpenSSLCertUtilsTest, TestX509CN) {
   auto x509 = readCertFromFile(kTestCertWithoutSan);
   EXPECT_NE(x509, nullptr);
-  auto identity = folly::ssl::OpenSSLCertUtils::getCommonName(*x509);
-  EXPECT_EQ(identity.value(), "Asox Company");
+  auto cn = folly::ssl::OpenSSLCertUtils::getCommonName(*x509);
+  EXPECT_EQ(cn.value(), "Asox Company");
   auto sans = folly::ssl::OpenSSLCertUtils::getSubjectAltNames(*x509);
   EXPECT_EQ(sans.size(), 0);
 }