x = some_range | reversed_evens; 2 110Range Adaptor Closure Objects [24.7.2.1] A range adaptor closure object is a . For a range adaptor closure object C and an expression R such that decltype((R)) argument and returns a view C(R) R | C 111Range Adaptor Closure Objects [24.7.2.1] A range adaptor closure object is a . For a range adaptor closure object C and an expression R such that decltype((R)) and returns a view view C(R) R | C 111Range Adaptor Closure Objects [24.7.2.1] A range adaptor closure object is a . For a range adaptor closure object C and an expression R such that decltype((R))

language a bit carefully to distinguish between: a lambda expression (the code that we write) a closure object (the object the compiler generates by evaluating the lambda expression)DEDUCING this AND LAMBDAS (Despite what cppinsights tells you…)CLOSURE OBJECTS, PER THE STANDARD "An implementation may define the closure object differently…" In particular, closure objects have:CLOSURE OBJECTS, PER THE STANDARD "An implementation may define the closure object differently…" In particular, closure objects have: no defined layoutCLOSURE OBJECTS, PER THE STANDARD "An implementation may define the closure object differently…"

sample(gen) ➡ view ❌ What do we need to fix? sample(gen) ➡ C (range adaptor closure object) If C is a range adaptor closure object and R is a range, these two expressions are equivalent: C(R) R | C std::ranges::range_adaptor_closure (C++23) template class sample_closure : public std::ranges::range_adaptor_closureclosure> { public: explicit sample_closure(RNG& gen) : gen_{gen} std::ranges::range_adaptor_closure (C++23) template class sample_closure : public std::ranges::range_adaptor_closureclosure> { public: explicit sample_closure(RNG& gen) : gen_{gen}

variable name ○ a closure is simply a function object . . . ■ which is returned from the evaluation of a lambda expression ■ myLamb contains the closure ■ deduced type is a “closure data type” auto expression is evaluated ■ ensure captured lvalue references remain alive for the entire lifetime of the closure auto myLamb = [&x] ( ) { return ++x; }; 20Lambda Expressions ● Capture Clause ○ C++11 ■ capture of evaluating a lambda expression which does not capture anything as a special kind of closure ■ special closure has no state so it can be implicitly converted to a function pointer ■ if you are calling

Rust 有安全保证，也需要测试确保 程序逻辑正确。第十二章中将会构建我们自己的 grep 命令行工具的功能子集实现，用于在文 件中搜索文本。为此会用到之前章节讨论的很多概念。 第十三章探索闭包（closure）和迭代器（iterator），这两个 Rust 特性来自函数式编程语言。 第十四章会深入探讨 Cargo 并介绍分享代码库的最佳实践。第十五章讨论标准库提供的智能 指针以及相关的 trait。 在的错误会使程 序 panic。 使用 match 处理 Result 的替代方案 这里有好多 match！match 确实很强大，不过也非常的原始。第十三章我们会介绍闭 包（closure），它会和定义在 Result 中的很多方法一起使用。在处理代码中的 Result 值时，使用这些方法往往比直接写 match 更简洁。 例如，这是另一个编写与示例 9-5 可以进行一些自定义的非 panic! 的错误处理。当 Result 是 Ok 时，这个方法的行为类似于 unwrap：它返回 Ok 内部封装的值。然而，当其值是 Err 时，该方法会调用一个闭包（closure），也就是一个我们定义的作为参数传递给 unwrap_or_else 的匿名函数。第十三章会更详细地介绍闭包。现在你需要理解的是 unwrap_or_else 会将 Err 的内部值，也就是示例

1: // namespace maybe::views 2: 3: template 4: constexpr /* maybe adaptor closure*/ transform(Callable&& c); 01: // namespace maybe 02: 03: template 04: concept not_void maybe::views 2: 3: template 4: constexpr /* maybe adaptor closure*/ transform(Callable&& c); 1: auto closure = maybe::views::transform(f1) 2: | maybe::views::and_then(f2) 3: initialization */}; 6: auto res = closure(mbObj); // res is our or_else view 7: std::cout << "res=" << *res << std::endl; 8: 9: auto asOpt = res | maybe::to; mbobj | closure;© 2018 Bloomberg Finance

is an output side effect ● filter contains state with the variable that is initialized in the closure ○ Running filter multiple times with the same input returns different outputs ● filter_timeseries argument int result = multiplyBy2(3); std::cout << result << std::endl; // Output: 6 } ● A closure is a function object that has an environment of its own, which keeps track of the variables captured std::endl; // Output: 6 } ● A closure is a function object that has an environment of its own, which keeps track of the variables captured from the outer scope ○ A closure can access and manipulate these

task); void add_peer(const PeerId& peer, Closure* done); void remove_peer(const PeerId& peer, Closure* done); void change_peers(const Configuration& new_peers, Closure* done); StateMachine void on_apply(::raft::Iterator& on_apply(::raft::Iterator& iter); void on_snapshot_save(SnapshotWriter* writer, Closure* done); int on_snapshot_load(SnapshotReader* reader); void on_leader_start(int64_t term); void on_leader_stop(const butil::Status&

shared reference to the closure, which means the closure can be executed repeatedly and even concurrently . An FnMut (e.g. accumulate) might mutate captured values. The closure object is accessed via exclusive concurrently . If you have an FnOnce (e.g. multiply_sum), you may only call it once. Doing so consumes the closure and any values captured by move . 107 FnMut � � � � � � � � � � � FnOnce � � � . Fn � � � � � � FnOnce � � � � � � � � � � � � � � � � � � . � � � � � � � � � � � � � � � � � � � � � � � � � � � closure � � � � � � � � � � � � � � � FnOnce � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

shared reference to the closure, which means the closure can be executed repeatedly and even concurrently. An FnMut (e.g. accumulate) might mutate captured values. The closure object is accessed via exclusive concurrently. If you have an FnOnce (e.g. multiply_sum), you may only call it once. Doing so consumes the closure and any values captured by move. FnMut is a subtype of FnOnce. Fn is a subtype of FnMut and FnOnce takes a closure, you should take FnOnce if you can (i.e. you call it once), or FnMut else, and last Fn. This allows the most flexibility for the caller. 104 In contrast, when you have a closure, the most