## DEDUCING this PATTERNS  BEN DEANE / @ben_deane CPPCON 2021 ## OVERVIEW This presentation is about P0847, "Deducing Gašper Ažman, Sy Brand, Ben Deane, Barry Revzin "We propose a new mechanism for specifying or deducing the value category of the expression that a member-function is invoked on. In other words, a way write) - a closure object (the object the compiler generates by evaluating the lambda expression) ## DEDUCING this AND LAMBDAS First, uniformity of syntax between regular member functions and lambda expressions

CTAD? ## Deducing function-template template argument template void myFunc(const T&){} myFunc(1); // invokes myFunc specialisation ## Deducing function-template T&){} myFunc(1); // deduces T = int, invokes myFunc specialisation ## Deducing function-template template argument template void myFunc(const T&){} Template deduction myFunc(1); // deduces T = int, invokes myFunc specialisation ## Deducing class-template template argument - pre C++17 template struct myStruct myStruct(const

Network Connection ## Derived 1 TCP ## Derived 2 UDP ## Timeline ## V irtual Functions • ~1986 ## Deducing This • C++23 ## Curiously Recurring Template Pattern (CRTP) • ~1995 ## Original Trend – Virtual ed*> ## New Trend – Explicit Object Parameter/Deducing This C++23 Feature • Simplifies Compile Time Polymorphism ## New Code – Deducing This struct NetworkConnection { public: void returned: 0 tcp tcp ## Multi-Level Inheritance – Deducing This Attempt // https://godbolt.org/z/ccsoaf3ec struct NetworkConnection void init(this auto&&

d/p27_2.jpg) Ben Deane Deducing this Patterns ## The Future of CRTP?  Ben Deane Deducing this Patterns ## CRTP Pre /b/2/a/2/b2a240cc83d862dcb67951e72bae578d/p32_2.jpg) ## C++23: Explicit Object Parameter AKA, Deducing This struct Shape { template void draw(this T&& self) { self.draw_impl();  ## Ben Deane Deducing this Patterns ## OK, THAT WAS A SIMPLE WIN There's more. Template deduction is unchanged.

Feature complete • C++23 • Deducing this (compiler support) • • std::expected • Many ranges features Coming next for C++23 • Standard library modules • Deducing this (modules support) std::print • Ranges: • to • zip and enumerate • cartesian product ## Coming next for C++23 • Deducing this (modules support) • 9 remaining C++ STL features ## Announcing In Visual Studio 2022 version

CPs Methods  + @@ Deducing this removes the need for CRTP ## Part II: An Overview Of CPs Methods • C++ was “born” with Customization >InheritanceCTSCPs (ADL)CPOsConcepts (+nominal)Deducing Thistag_invokeCustom functionsReflection0 码力 | 58 页 | 18.82 MB | 1 年前

be avoided by delegating to helper methods → Cumbersome ☐ C++23: ☐ Explicit object parameters → deducing this ☐ Replace all 3 overloads with: template auto&& GetName(this in a lambda accesses the object that contains the lambda, not the lambda instance itself! ☐ With deducing this: auto fibonacci = [](this auto self, int n) { if (n < 2) { return n; } return self(n

wait_for( Power::isAwake ); ## C++23: Explicit Object Parameter AKA, Deducing This struct Shape { template void draw(this T&& self) { self.draw_impl();

> ## PARTIAL APPLICATION, C++ STYLE (Now you see one of my personal incentives for P0847 Deducing this) See also C++Weekly Episode 318: My Meetup Got Nerd Sniped! Tip: attend your local meetup

with the same key always produces a unique cipher text. The idea is to prevent the attacker from deducing information from repeated patterns in the encrypted data. From the provided alternatives, the default