## +23 ## Back To Basics Forwarding References ## MATEUSZ PUSZ ## 20 23 October 01 - 06 ## Workshop Style ## Workshop Style • Provide rationale • Facilitate discussion - force the audience to provided by the function that is being called with the argument of an rvalue reference type ## Forwarding reference • Deduced function template parameter declared as rvalue reference to cv-unqualified parameter template void f(T&& x); void f(auto&& x); ## Forwarding reference • Deduced function template parameter declared as rvalue reference to cv-unqualified

THINK OPEN 开放性思维 ## Apache OpenWhisk + Kubernetes: A Perfect Match for Your Serverless Platform Ying Chun Guo guoyingc@cn.ibm.com Zhou Xing xingzhou@qiyi.com ## Agenda • What is serverless? • Kubernetes

iosuttis | eckstein 33 IT communication ## C++ Move Semantics ## Perfect Forwarding 34 ## Motivation for Perfect Forwarding 1/2 ## • Overloading for const/non-const lvalues and rvalues: class // calls foo(C(&)) C++ 35 josuttis | eckstein IT communication ## Motivation for Perfect Forwarding 2/2 ## • Forward move semantics in helper functions: class C { }; void foo(const C&); // calls foo(C&&) C++ 36 josuttis | eckstein IT communication ## Perfect Forwarding • Perfect forwarding of parameters: 1. Template parameter 2. Declaring the parameter as && of

some_extra_function(); - can change the referenced value return copy == x; ## Perfect forwarding ### “In C++, perfect forwarding is the act of passing a function’s parameters to another function while preserving std::unique_ptr( new T(std::forward(args) ...)); ## Perfect forwarding is not perfect! ### “In C++, perfect forwarding is the act of passing a function’s parameters to another function while T(std::forward(args)...)); breaks RVO ## Perfect forwarding is not perfect! “In C++, perfect forwarding is the act of passing a function’s parameters to another function while

xvalue ..... 41 rvalue reference and lvalue reference ..... 43 Move semantics ..... 45 Perfect forwarding ..... 47 Conclusion ..... 50 Further Readings ..... 50 Chapter 04 Containers ..... 50 slightly more complicated use of C++14. To understand it you need to know the concept of parameter forwarding in C++, which we will cover in detail in the Language Runtime Enhancements chapter, and you can this section later. In simple terms, decltype(auto) is mainly used to derive the return type of a forwarding function or package, which does not require us to explicitly specify the parameter expression of

cyclic references), objects with shared ownership may never be deleted. • Smart pointers are not perfect substitutes for plain pointers. If dynamic allocation is necessary, prefer to keep ownership with errors. cpplint.py is a tool that reads a source file and identifies many style errors. It is not perfect, and has both false positives and false negatives, but it is still a valuable tool. False positives Use rvalue references only to define move constructors and move assignment operators, or for perfect forwarding. Rvalue references are a type of reference that can only bind to temporary objects. The syntax

[Image](/uploads/documents/4/b/9/5/4b95bf300a331d697987567a8b905024/p154_2.jpg) Figure 38. Fast-forwarding the master branch Now, the snapshot pointed to by C4' is exactly the same as the one that a topic branch off another topic branch Now you can fast-forward your master branch (see Fast-forwarding your master branch to include the client branch changes): $ git checkout master $ git merge client [Image](/uploads/documents/4/b/9/5/4b95bf300a331d697987567a8b905024/p157_1.jpg) Figure 41. Fast-forwarding your master branch to include the client branch changes Let's say you decide to pull in your

implement some logic, which may make it difficult to read and maintain in the future. This is the perfect time to use the switch statement to solve this problem. switch sExpr { case expr1: some which depends on the local DNS server's settings. -If the local DNS server doesn't enable forwarding, it routes the request to the root DNS server, then returns the IP address of a top level DNS server next level DNS server for the IP address corresponding to www.qq.com. -If the local DNS server has forwarding enabled, it sends the request to an upper level DNS server. If the upper level DNS server also

[Image](/uploads/documents/d/0/e/1/d0e1c20f22394ebaac3f3dee178f01a0/p103_1.jpg) Figure 38. Fast-forwarding the master branch Now, the snapshot pointed to by C4' is exactly the same as the one that branch (see Fast-forwarding your master branch to include the client branch changes):  Figure 41. Fast-forwarding your master execute access. Connection to gitserver closed. At this point, users are still able to use SSH port forwarding to access any host the git server is able to reach. If you want to prevent that, you can edit the

[Image](/uploads/documents/b/2/0/7/b207007df3e5c384de7c178d309c361a/p146_2.jpg) Figure 38. Fast-forwarding the master branch Now, the snapshot pointed to by C4' is exactly the same as the one that a topic branch off another topic branch Now you can fast-forward your master branch (see Fast-forwarding your master branch to include the client branch changes): $ git checkout master $ git merge client [Image](/uploads/documents/b/2/0/7/b207007df3e5c384de7c178d309c361a/p149_1.jpg) Figure 41. Fast-forwarding your master branch to include the client branch changes Let's say you decide to pull in your