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Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.
77/2010 · 201

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Returns:;; The number of elements visited (0 or 1). Notes:;; The `template<class K, class F>` overloads only participate in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.
返回值：访问过的元素数量（0 或 1）。
注意：template<class k,="" class="" f=""> 形式的重载仅在 Hash::is_transparent 与 Pred::is_transparent 为合法成员别名时才参与重载决议。
库假定 Hash 可同时用于 K 类型与 Key 类型，且 Pred 是透明的。
这支持异构查找，避免了实例化 Key 类型对象带来的开销。</class>
:788
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Bulk visit
批量访问
```c++ template<class FwdIterator, class F> size_t visit(FwdIterator first, FwdIterator last, F f); template<class FwdIterator, class F> size_t visit(FwdIterator first, FwdIterator last, F f) const; template<class FwdIterator, class F> size_t cvisit(FwdIterator first, FwdIterator last, F f) const; ```
```c++ template<class fwditerator,="" class="" f=""> size_t visit(FwdIterator first, FwdIterator last, F f); template<class fwditerator,="" class="" f=""> size_t visit(FwdIterator first, FwdIterator last, F f) const; template<class fwditerator,="" class="" f=""> size_t cvisit(FwdIterator first, FwdIterator last, F f) const; ```</class></class></class>
For each element `k` in the range [`first`, `last`), if there is an element `x` in the container with key equivalent to `k`, invokes `f` with a reference to `x`. Such reference is const iff `*this` is const.
对范围 [first, last) 中的每个键 k：
如果容器中存在键与 k 等价的元素 x，则以 x 的引用调用函数 f。
当且仅当当前容器 *this 为常量（const）时，该引用为常量引用。
Although functionally equivalent to individually invoking xref:concurrent_flat_map_cvisit[`[c\]visit`] for each key, bulk visitation performs generally faster due to internal streamlining optimizations. It is advisable that `std::distance(first,last)` be at least xref:#concurrent_flat_map_constants[`bulk_visit_size`] to enjoy a performance gain: beyond this size, performance is not expected to increase further.
尽管功能上等价于对每个键单独调用 [c]visit，但批量访问因内部流线型优化，通常性能更高。
建议 std::distance(first,last) 至少达到 bulk_visit_size 阈值时再使用，以获得性能提升；超过该大小后，性能不会进一步提升。
Requires:;; `FwdIterator` is a https://en.cppreference.com/w/cpp/named_req/ForwardIterator[LegacyForwardIterator^] ({cpp}11 to {cpp}17), or satisfies https://en.cppreference.com/w/cpp/iterator/forward_iterator[std::forward_iterator^] ({cpp}20 and later). For `K` = `std::iterator_traits<FwdIterator>::value_type`, either `K` is `key_type` or else `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. In the latter case, the library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. Returns:;; The number of elements visited.
要求：`FwdIterator` 需满足 https://en.cppreference.com/w/cpp/named_req/ForwardIterator[遗留向前迭代器^] 要求（{cpp}11 至 {cpp}17），或满足 https://en.cppreference.com/w/cpp/iterator/forward_iterator[`std::forward_iterator`^] 要求（{cpp}20 及更高版本）。对于 `K = std::iterator_traits<fwditerator>::value_type`，要么 `K` 是 `key_type`，要么 `Hash::is_transparent` 和 `Pred::is_transparent` 是有效的成员 typedef。在后一种情况下，库假定 `Hash` 可同时以 `K` 和 `Key` 调用，且 `Pred` 是透明的。该机制支持异构查找，从而避免实例化 `Key` 类型的开销。返回：被访问的元素数量。</fwditerator>
:824
---
---
[c]visit_all
[c]visit_all
```c++ template<class F> size_t visit_all(F f); template<class F> size_t visit_all(F f) const; template<class F> size_t cvisit_all(F f) const; ```
```c++ template<class f=""> size_t visit_all(F f); template<class f=""> size_t visit_all(F f) const; template<class f=""> size_t cvisit_all(F f) const; ```</class></class></class>
Successively invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const.
依次以表中每个元素的引用调用函数 f。
当且仅当当前容器 *this 为常量（const）时，该引用为常量引用。
Returns:;; The number of elements visited.
返回值：访问到的元素数量。
:840
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---
Parallel [c]visit_all
并行 [c]visit_all
```c++ template<class ExecutionPolicy, class F> void visit_all(ExecutionPolicy&& policy, F f); template<class ExecutionPolicy, class F> void visit_all(ExecutionPolicy&& policy, F f) const; template<class ExecutionPolicy, class F> void cvisit_all(ExecutionPolicy&& policy, F f) const; ```
```c++ template<class executionpolicy,="" class="" f=""> void visit_all(ExecutionPolicy&amp;&amp; policy, F f); template<class executionpolicy,="" class="" f=""> void visit_all(ExecutionPolicy&amp;&amp; policy, F f) const; template<class executionpolicy,="" class="" f=""> void cvisit_all(ExecutionPolicy&amp;&amp; policy, F f) const; ```</class></class></class>
Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.
以表中每个元素的引用调用函数 f。
当且仅当当前容器 *this 为常量（const）时，该引用为常量引用。
执行过程将根据指定的执行策略语义进行并行化。
Throws:;; Depending on the exception handling mechanism of the execution policy used, may call `std::terminate` if an exception is thrown within `f`. Notes:;; Only available in compilers supporting C++17 parallel algorithms. + + These overloads only participate in overload resolution if `std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>` is `true`. + + Unsequenced execution policies are not allowed.
抛出异常：根据所使用执行策略的异常处理机制，如果 f 内部抛出异常，则可能会调用 std::terminate。
注意：仅在支持 C++17 并行算法的编译器中可用。
仅当 std::is_execution_policy_v<std::remove_cvref_t<executionpolicy>&gt; 为 true 时，这些重载版本才参与重载决议。
不允许使用无序执行策略。</std::remove_cvref_t<executionpolicy>
:861
---
---
[c]visit_while
[c]visit_while
```c++ template<class F> bool visit_while(F f); template<class F> bool visit_while(F f) const; template<class F> bool cvisit_while(F f) const; ```
```c++ template<class f=""> bool visit_while(F f); template<class f=""> bool visit_while(F f) const; template<class f=""> bool cvisit_while(F f) const; ```</class></class></class>
Successively invokes `f` with references to each of the elements in the table until `f` returns `false` or all the elements are visited. Such references to the elements are const iff `*this` is const.
依次以表中每个元素的引用调用函数 f，直到 f 返回 false 或遍历完所有元素。
当且仅当当前容器 *this 为常量（const）时，该元素引用为常量引用。
Returns:;; `false` iff `f` ever returns `false`.
返回值：当且仅当 f 曾返回 false 时，整体返回 false。
:878
---
---
Parallel [c]visit_while
并行 [c]visit_while
```c++ template<class ExecutionPolicy, class F> bool visit_while(ExecutionPolicy&& policy, F f); template<class ExecutionPolicy, class F> bool visit_while(ExecutionPolicy&& policy, F f) const; template<class ExecutionPolicy, class F> bool cvisit_while(ExecutionPolicy&& policy, F f) const; ```
```c++ template<class executionpolicy,="" class="" f=""> bool visit_while(ExecutionPolicy&amp;&amp; policy, F f); template<class executionpolicy,="" class="" f=""> bool visit_while(ExecutionPolicy&amp;&amp; policy, F f) const; template<class executionpolicy,="" class="" f=""> bool cvisit_while(ExecutionPolicy&amp;&amp; policy, F f) const; ```</class></class></class>
Invokes `f` with references to each of the elements in the table until `f` returns `false` or all the elements are visited. Such references to the elements are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.
以表中每个元素的引用调用函数 f，直到 f 返回 false 或遍历完所有元素。
当且仅当当前容器 *this 为常量（const）时，该元素引用为常量引用。
执行过程将根据指定的执行策略语义进行并行化。
Returns:;; `false` iff `f` ever returns `false`. Throws:;; Depending on the exception handling mechanism of the execution policy used, may call `std::terminate` if an exception is thrown within `f`. Notes:;; Only available in compilers supporting C++17 parallel algorithms. + + These overloads only participate in overload resolution if `std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>` is `true`. + + Unsequenced execution policies are not allowed. + + Parallelization implies that execution does not necessary finish as soon as `f` returns `false`, and as a result `f` may be invoked with further elements for which the return value is also `false`.
返回值：当且仅当 f 曾返回 false 时，整体返回 false。
抛出异常：根据所使用执行策略的异常处理机制，如果 f 内部抛出异常，则可能会调用 std::terminate。
注意：
仅在支持 C++17 并行算法的编译器中可用。
仅当 std::is_execution_policy_v<std::remove_cvref_t<executionpolicy>&gt; 为 true 时，这些重载版本才参与重载决议。
不允许使用无序执行策略。
并行化意味着：即使 f 已返回 false，执行流程也不一定会立即终止；因此，f 可能还会被继续调用以处理后续元素，且这些调用同样可能返回 false。</std::remove_cvref_t<executionpolicy>
:905
---
---
Size and Capacity
大小与容量
empty
空
```c++ [[nodiscard]] bool empty() const noexcept; ```
```c++ [[nodiscard]] bool empty() const noexcept; ```
English Chinese (Simplified Han script) Actions
Assign from values in initializer list. All previously existing elements are destroyed.
并发：阻塞于 *this 和 other。
从初始化列表赋值。销毁所有先前存在的元素。
Visitation
访问操作
[c]visit
[c]visit
```c++ template<class F> size_t visit(const key_type& k, F f); template<class F> size_t visit(const key_type& k, F f) const; template<class F> size_t cvisit(const key_type& k, F f) const; template<class K, class F> size_t visit(const K& k, F f); template<class K, class F> size_t visit(const K& k, F f) const; template<class K, class F> size_t cvisit(const K& k, F f) const; ```
```c++ template<class f=""> size_t visit(const key_type&amp; k, F f); template<class f=""> size_t visit(const key_type&amp; k, F f) const; template<class f=""> size_t cvisit(const key_type&amp; k, F f) const; template<class k,="" class="" f=""> size_t visit(const K&amp; k, F f); template<class k,="" class="" f=""> size_t visit(const K&amp; k, F f) const; template<class k,="" class="" f=""> size_t cvisit(const K&amp; k, F f) const; ```</class></class></class></class></class></class>
If an element `x` exists with key equivalent to `k`, invokes `f` with a reference to `x`. Such reference is const iff `*this` is const.
若存在键与 k 等价的元素 x，则以 x 的引用调用函数 f。
当且仅当当前容器 *this 为常量（const）时，该引用为常量引用。
Returns:;; The number of elements visited (0 or 1). Notes:;; The `template<class K, class F>` overloads only participate in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type.
返回值：访问过的元素数量（0 或 1）。
注意：template<class k,="" class="" f=""> 形式的重载仅在 Hash::is_transparent 与 Pred::is_transparent 为合法成员别名时才参与重载决议。
库假定 Hash 可同时用于 K 类型与 Key 类型，且 Pred 是透明的。
这支持异构查找，避免了实例化 Key 类型对象带来的开销。</class>
Bulk visit
批量访问
```c++ template<class FwdIterator, class F> size_t visit(FwdIterator first, FwdIterator last, F f); template<class FwdIterator, class F> size_t visit(FwdIterator first, FwdIterator last, F f) const; template<class FwdIterator, class F> size_t cvisit(FwdIterator first, FwdIterator last, F f) const; ```
```c++ template<class fwditerator,="" class="" f=""> size_t visit(FwdIterator first, FwdIterator last, F f); template<class fwditerator,="" class="" f=""> size_t visit(FwdIterator first, FwdIterator last, F f) const; template<class fwditerator,="" class="" f=""> size_t cvisit(FwdIterator first, FwdIterator last, F f) const; ```</class></class></class>
Requires:;; `FwdIterator` is a https://en.cppreference.com/w/cpp/named_req/ForwardIterator[LegacyForwardIterator^] ({cpp}11 to {cpp}17), or satisfies https://en.cppreference.com/w/cpp/iterator/forward_iterator[std::forward_iterator^] ({cpp}20 and later). For `K` = `std::iterator_traits<FwdIterator>::value_type`, either `K` is `key_type` or else `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. In the latter case, the library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. Returns:;; The number of elements visited.
要求：`FwdIterator` 需满足 https://en.cppreference.com/w/cpp/named_req/ForwardIterator[遗留向前迭代器^] 要求（{cpp}11 至 {cpp}17），或满足 https://en.cppreference.com/w/cpp/iterator/forward_iterator[`std::forward_iterator`^] 要求（{cpp}20 及更高版本）。对于 `K = std::iterator_traits<fwditerator>::value_type`，要么 `K` 是 `key_type`，要么 `Hash::is_transparent` 和 `Pred::is_transparent` 是有效的成员 typedef。在后一种情况下，库假定 `Hash` 可同时以 `K` 和 `Key` 调用，且 `Pred` 是透明的。该机制支持异构查找，从而避免实例化 `Key` 类型的开销。返回：被访问的元素数量。</fwditerator>
```c++ template<class F> size_t visit_all(F f); template<class F> size_t visit_all(F f) const; template<class F> size_t cvisit_all(F f) const; ```
```c++ template<class f=""> size_t visit_all(F f); template<class f=""> size_t visit_all(F f) const; template<class f=""> size_t cvisit_all(F f) const; ```</class></class></class>
Successively invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const.
依次以表中每个元素的引用调用函数 f。
当且仅当当前容器 *this 为常量（const）时，该引用为常量引用。
Returns:;; The number of elements visited.
返回值：访问到的元素数量。
Parallel [c]visit_all
并行 [c]visit_all
```c++ bool insert(const value_type& obj); bool insert(const init_type& obj); ```
```c++ bool insert(const value_type&amp; obj); bool insert(const init_type&amp; obj); ```
```c++ template<class ExecutionPolicy, class F> void visit_all(ExecutionPolicy&& policy, F f); template<class ExecutionPolicy, class F> void visit_all(ExecutionPolicy&& policy, F f) const; template<class ExecutionPolicy, class F> void cvisit_all(ExecutionPolicy&& policy, F f) const; ```
```c++ template<class executionpolicy,="" class="" f=""> void visit_all(ExecutionPolicy&amp;&amp; policy, F f); template<class executionpolicy,="" class="" f=""> void visit_all(ExecutionPolicy&amp;&amp; policy, F f) const; template<class executionpolicy,="" class="" f=""> void cvisit_all(ExecutionPolicy&amp;&amp; policy, F f) const; ```</class></class></class>
Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.
以表中每个元素的引用调用函数 f。
当且仅当当前容器 *this 为常量（const）时，该引用为常量引用。
执行过程将根据指定的执行策略语义进行并行化。
Throws:;; Depending on the exception handling mechanism of the execution policy used, may call `std::terminate` if an exception is thrown within `f`. Notes:;; Only available in compilers supporting C++17 parallel algorithms. + + These overloads only participate in overload resolution if `std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>` is `true`. + + Unsequenced execution policies are not allowed.
抛出异常：根据所使用执行策略的异常处理机制，如果 f 内部抛出异常，则可能会调用 std::terminate。
注意：仅在支持 C++17 并行算法的编译器中可用。
仅当 std::is_execution_policy_v<std::remove_cvref_t<executionpolicy>&gt; 为 true 时，这些重载版本才参与重载决议。
不允许使用无序执行策略。</std::remove_cvref_t<executionpolicy>
[c]visit_while
[c]visit_while
Successively invokes `f` with references to each of the elements in the table until `f` returns `false` or all the elements are visited. Such references to the elements are const iff `*this` is const.
依次以表中每个元素的引用调用函数 f，直到 f 返回 false 或遍历完所有元素。
当且仅当当前容器 *this 为常量（const）时，该元素引用为常量引用。
Parallel [c]visit_while
并行 [c]visit_while
```c++ template<class ExecutionPolicy, class F> bool visit_while(ExecutionPolicy&& policy, F f); template<class ExecutionPolicy, class F> bool visit_while(ExecutionPolicy&& policy, F f) const; template<class ExecutionPolicy, class F> bool cvisit_while(ExecutionPolicy&& policy, F f) const; ```
```c++ template<class executionpolicy,="" class="" f=""> bool visit_while(ExecutionPolicy&amp;&amp; policy, F f); template<class executionpolicy,="" class="" f=""> bool visit_while(ExecutionPolicy&amp;&amp; policy, F f) const; template<class executionpolicy,="" class="" f=""> bool cvisit_while(ExecutionPolicy&amp;&amp; policy, F f) const; ```</class></class></class>
Returns:;; `false` iff `f` ever returns `false`. Throws:;; Depending on the exception handling mechanism of the execution policy used, may call `std::terminate` if an exception is thrown within `f`. Notes:;; Only available in compilers supporting C++17 parallel algorithms. + + These overloads only participate in overload resolution if `std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>` is `true`. + + Unsequenced execution policies are not allowed. + + Parallelization implies that execution does not necessary finish as soon as `f` returns `false`, and as a result `f` may be invoked with further elements for which the return value is also `false`.
返回值：当且仅当 f 曾返回 false 时，整体返回 false。
抛出异常：根据所使用执行策略的异常处理机制，如果 f 内部抛出异常，则可能会调用 std::terminate。
注意：
仅在支持 C++17 并行算法的编译器中可用。
仅当 std::is_execution_policy_v<std::remove_cvref_t<executionpolicy>&gt; 为 true 时，这些重载版本才参与重载决议。
不允许使用无序执行策略。
并行化意味着：即使 f 已返回 false，执行流程也不一定会立即终止；因此，f 可能还会被继续调用以处理后续元素，且这些调用同样可能返回 false。</std::remove_cvref_t<executionpolicy>
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; Invalidates pointers and references to elements if a rehashing is issued. + + A call of the form `insert(x)`, where `x` is equally convertible to both `const value_type&` and `const init_type&`, is not ambiguous and selects the `init_type` overload.
要求：`value_type` 需满足 https://en.cppreference.com/w/cpp/named_req/CopyInsertable[可复制插入^] 要求。返回：若执行了插入则返回 `true`。并发：在 `*this` 的 rehash 操作上阻塞。注意：如果执行了 rehash，则指向元素的指针和引用会失效。+ +形式为 `insert(x)` 的调用（其中 `x` 可同等转换为 `const value_type&amp;` 和 `const init_type&amp;`）不会产生歧义，并且会选择 `init_type` 重载。
Move Insert
移动插入
```c++ bool insert(value_type&& obj); bool insert(init_type&& obj); ```
```c++ bool insert(value_type&amp;&amp; obj); bool insert(init_type&amp;&amp; obj); ```
Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; `true` if an insert took place. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; Invalidates pointers and references to elements if a rehashing is issued. + + A call of the form `insert(x)`, where `x` is equally convertible to both `value_type&&` and `init_type&&`, is not ambiguous and selects the `init_type` overload.
要求：`value_type` 需满足 https://en.cppreference.com/w/cpp/named_req/MoveInsertable[可移动插入^] 要求。返回：若执行了插入则返回 `true`。并发：在 `*this` 的 rehash 操作上阻塞。注意：如果执行了 rehash，则指向元素的指针和引用会失效。+ +形式为 `insert(x)` 的调用（其中 `x` 可同等转换为 `value_type&amp;&amp;` 和 `init_type&amp;&amp;`）不会产生歧义，并且会选择 `init_type` 重载。
```c++ template<class InputIterator> size_type insert(InputIterator first, InputIterator last); ```
```c++ template<class inputiterator=""> size_type insert(InputIterator first, InputIterator last); ```</class>
```c++ template<class... Args, class F> bool emplace_or_visit(Args&&... args, F&& f); template<class... Args, class F> bool emplace_or_cvisit(Args&&... args, F&& f); ```
```c++ template<class... args,="" class="" f=""> bool emplace_or_visit(Args&amp;&amp;... args, F&amp;&amp; f); template<class... args,="" class="" f=""> bool emplace_or_cvisit(Args&amp;&amp;... args, F&amp;&amp; f); ```</class...></class...>
Inserts an object, constructed with the arguments `args`, in the table if there is no element in the table with an equivalent key. Otherwise, invokes `f` with a reference to the equivalent element; such reference is const iff `emplace_or_cvisit` is used.
若容器中无等价键的元素，则使用参数 args 构造对象并插入容器；
否则，将等价元素的引用传递给函数 f 并调用 —— 若使用的是 emplace_or_cvisit，则该引用为常量引用。
Requires:;; `value_type` is constructible from `args`. Returns:;; `true` if an insert took place. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; Invalidates pointers and references to elements if a rehashing is issued. + + The interface is exposition only, as C++ does not allow to declare a parameter `f` after a variadic parameter pack.
要求：`value_type` 可从 `args` 构造。返回：若执行了插入则返回 `true`。并发：在 `*this` 的 rehash 操作上阻塞。注意：如果执行了 rehash，则指向元素的指针和引用会失效。+ +该接口仅为展示说明，因为 C++ 不允许在变参参数包之后声明参数 `f`。

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Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.
Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.以表中每个元素的引用调用函数 f。
当且仅当当前容器 *this 为常量（const）时，该引用为常量引用。
执行过程将根据指定的执行策略语义进行并行化。
06/05/2026
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Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.
Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified.
06/05/2026
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Flags
safe-html, strict-same
Unit identifier
53876
Source string location
:850
String age
06/05/2026
Last updated
06/06/2026
Source string age
06/05/2026
Translation file AsciiDoc file
doc/modules/ROOT/pages/reference/concurrent_flat_map_zh_Hans.adoc, string 179