1650 strings

Translation Key Source string Target string
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
Value Type: https://github.com/nlohmann/json/blob/00cb98a3d170161711ab912ae6acefba31f29f75/include/nlohmann/json.hpp#L165[`nlohmann::basic_json`]
Value Type: https://github.com/nlohmann/json/blob/00cb98a3d170161711ab912ae6acefba31f29f75/include/nlohmann/json.hpp#L165[`nlohmann::basic_json`]
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
This library adopts a "kitchen sink" approach. It contains a wealth of features, even those with niche uses. Its weakness is that the many template parameters, while allowing for configurability, inhibit the best possible optimizations. The consequence is that the library performs poorly. The ability to configure every aspect of the value type has the paradoxical effect of making it less suitable as a vocabulary type.
This library adopts a "kitchen sink" approach. It contains a wealth of features, even those with niche uses. Its weakness is that the many template parameters, while allowing for configurability, inhibit the best possible optimizations. The consequence is that the library performs poorly. The ability to configure every aspect of the value type has the paradoxical effect of making it less suitable as a vocabulary type.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} `basic_json` is a class template. Libraries must agree on the
{icon_bad} `basic_json` is a class template. Libraries must agree on the
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
choices of template parameters to be interoperable.
choices of template parameters to be interoperable.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Too much customization. We struggle to see a use case for making
{icon_bad} Too much customization. We struggle to see a use case for making
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
`BooleanType` anything other than `bool`.
`BooleanType` anything other than `bool`.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Poor separation of concerns. The `basic_json` container
{icon_bad} Poor separation of concerns. The `basic_json` container
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
declaration needlessly conflates parsing and serialization APIs.
declaration needlessly conflates parsing and serialization APIs.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Limited allocator support. Only stateless allocators are allowed,
{icon_bad} Limited allocator support. Only stateless allocators are allowed,
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
which rules out the most important type of allocator, a local arena-based implementation.
which rules out the most important type of allocator, a local arena-based implementation.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
:70
{icon_bad} No incremental parsing, no incremental serialization.
{icon_bad} No incremental parsing, no incremental serialization.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Slow parsing and serialization performance.
{icon_bad} Slow parsing and serialization performance.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_good} Full-featured, including JSON Pointer, CBOR, and others.
{icon_good} Full-featured, including JSON Pointer, CBOR, and others.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
Comparison to RapidJSON
Comparison to RapidJSON
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
Value Type: https://github.com/Tencent/rapidjson/blob/bb5f966b9939d6cdfbac3462a0410e185099b3af/include/rapidjson/document.h#L608[`rapidjson::GenericValue`]
Value Type: https://github.com/Tencent/rapidjson/blob/bb5f966b9939d6cdfbac3462a0410e185099b3af/include/rapidjson/document.h#L608[`rapidjson::GenericValue`]
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} The value type is not regular. Assignment is destructive,
{icon_bad} The value type is not regular. Assignment is destructive,
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
performing `a = b` is equivalent to `a = std::move(b)`. No copy construction or copy assignment allowed.
performing `a = b` is equivalent to `a = std::move(b)`. No copy construction or copy assignment allowed.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Object types have no hash table or index to reduce the cost of
{icon_bad} Object types have no hash table or index to reduce the cost of
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
lookups.
lookups.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Allocators have reference semantics. Problems with lifetime are
{icon_bad} Allocators have reference semantics. Problems with lifetime are
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
easily encountered.
easily encountered.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} The interface of the array and object types are considerably
{icon_bad} The interface of the array and object types are considerably
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
different from their standard library equivalents, and not idiomatic.
different from their standard library equivalents, and not idiomatic.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
:106
{icon_bad} No incremental parsing, no incremental serialization.
{icon_bad} No incremental parsing, no incremental serialization.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_good} Parsing and serialization performance is better than most other
{icon_good} Parsing and serialization performance is better than most other
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
libraries.
libraries.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
Comparison to SIMD JSON
Comparison to SIMD JSON
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
This is quite an interesting data structure, which is optimized to work well with the SIMD parser. It makes very good design choices for the intended use-case. However it is not well suited as a vocabulary type due to the necessary limitations.
This is quite an interesting data structure, which is optimized to work well with the SIMD parser. It makes very good design choices for the intended use-case. However it is not well suited as a vocabulary type due to the necessary limitations.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Sequential access only, via `ParsedJson::BasicIterator`
{icon_bad} Sequential access only, via `ParsedJson::BasicIterator`
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_bad} Read-only, can only be populated by the provided SIMD JSON parser.
{icon_bad} Read-only, can only be populated by the provided SIMD JSON parser.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — English
{icon_good} The fastest available JSON parser.
{icon_good} The fastest available JSON parser.
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
= Comparison to Other Libraries
= 与其他库的比较
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
:icon_good: pass:q[[.green]##&#10004##] :icon_bad: pass:q[[.red]##&#10008##]
:icon_good: pass:q[[.green]##✔##] :icon_bad: pass:q[[.red]##✘##]
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
There exist many C++ JSON libraries, but two are particularly noteworthy for the purpose of comparison: https://rapidjson.org/[RapidJSON], https://nlohmann.github.io/json/[JSON for Modern {cpp}] (referred to herein as nlohmann's JSON, or nlohmann), and https://github.com/lemire/simdjson[SIMD JSON].
C++ 中存在众多 JSON 库，但为了比较的目的，有三个在对比中尤为值得关注：https://rapidjson.org/[RapidJSON]、https://nlohmann.github.io/json/[JSON for Modern {cpp}]（本文中称为 nlohmann's JSON， 或简称 nlohmann）以及https://github.com/lemire/simdjson[SIMD JSON]。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
Comparison to nlohmann JSON
与nlohmann JSON的比较
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
Value Type: https://github.com/nlohmann/json/blob/00cb98a3d170161711ab912ae6acefba31f29f75/include/nlohmann/json.hpp#L165[`nlohmann::basic_json`]
值类型：https://github.com/nlohmann/json/blob/00cb98a3d170161711ab912ae6acefba31f29f75/include/nlohmann/json.hpp#L165[`nlohmann::basic_json`]
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
This library adopts a "kitchen sink" approach. It contains a wealth of features, even those with niche uses. Its weakness is that the many template parameters, while allowing for configurability, inhibit the best possible optimizations. The consequence is that the library performs poorly. The ability to configure every aspect of the value type has the paradoxical effect of making it less suitable as a vocabulary type.
该库采用了一种“大而全”（kitchen sink）的设计理念，包含大量功能，甚至涵盖一些使用场景非常小众的特性。其弱点在于：尽管众多模板参数提供了高度可配置性，却阻碍了编译器实现最优的性能优化。其结果是性能表现较差。这种对值类型各方面均可配置的能力，反而使其作为通用类型的适用性降低，形成了一种悖论效应。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} `basic_json` is a class template. Libraries must agree on the
{icon_bad} `basic_json` 是一个类模板。各库必须在
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
choices of template parameters to be interoperable.
模板参数的选择上达成一致，这样才能实现互操作。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Too much customization. We struggle to see a use case for making
{icon_bad} 过度定制化。我们很难想象
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
`BooleanType` anything other than `bool`.
将 `BooleanType` 设置为 `bool` 之外的其他类型的使用场景。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Poor separation of concerns. The `basic_json` container
{icon_bad} 关注点分离不佳。`basic_json` 容器
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
declaration needlessly conflates parsing and serialization APIs.
声明不必要地将解析和序列化API混杂在一起。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Limited allocator support. Only stateless allocators are allowed,
{icon_bad} 分配器支持有限。只允许无状态分配器，
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
which rules out the most important type of allocator, a local arena-based implementation.
这排除了最重要的一类分配器，即基于本地内存池的实现。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
:70
{icon_bad} No incremental parsing, no incremental serialization.
{icon_bad} 没有增量式解析，也没有增量式序列化。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Slow parsing and serialization performance.
{icon_bad} 解析和序列化性能较差。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_good} Full-featured, including JSON Pointer, CBOR, and others.
{icon_good} 功能全面，包含 JSON Pointer、CBOR 等特性。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
Comparison to RapidJSON
与RapidJSON的比较
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
Value Type: https://github.com/Tencent/rapidjson/blob/bb5f966b9939d6cdfbac3462a0410e185099b3af/include/rapidjson/document.h#L608[`rapidjson::GenericValue`]
值类型：https://github.com/Tencent/rapidjson/blob/bb5f966b9939d6cdfbac3462a0410e185099b3af/include/rapidjson/document.h#L608[`rapidjson::GenericValue`]
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} The value type is not regular. Assignment is destructive,
{icon_bad} 值类型不满足“正规性”要求。赋值具有破坏性，
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
performing `a = b` is equivalent to `a = std::move(b)`. No copy construction or copy assignment allowed.
执行 `a = b` 等同于 `a = std::move(b)`，且不允许复制构造和复制赋值。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Object types have no hash table or index to reduce the cost of
{icon_bad} 对象类型没有哈希表或索引用于降低查找成本。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
lookups.
(查找。)
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Allocators have reference semantics. Problems with lifetime are
{icon_bad} 分配器采用引用语义，容易引发生命周期问题。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
easily encountered.
（容易引发。）
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} The interface of the array and object types are considerably
{icon_bad} 数组和对象类型的接口
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
different from their standard library equivalents, and not idiomatic.
与标准库中的对应类型差异显著，且不符合惯用法。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
:106
{icon_bad} No incremental parsing, no incremental serialization.
{icon_bad} 没有增量式解析，也没有增量式序列化。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_good} Parsing and serialization performance is better than most other
{icon_good} 解析和序列化性能优于大多数其他。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
libraries.
库。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
Comparison to SIMD JSON
与SIMD JSON的比较
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
This is quite an interesting data structure, which is optimized to work well with the SIMD parser. It makes very good design choices for the intended use-case. However it is not well suited as a vocabulary type due to the necessary limitations.
这是一种相当有趣的数据结构，专为与 SIMD 解析器协同工作而优化。它在目标使用场景下做出了非常优秀的设计选择。然而，由于其必要的限制，它不太适合作为通用类型。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Sequential access only, via `ParsedJson::BasicIterator`
{icon_bad} 仅支持通过 `ParsedJson::BasicIterator` 进行顺序访问
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_bad} Read-only, can only be populated by the provided SIMD JSON parser.
{icon_bad} 为只读类型，仅能通过所提供的 SIMD JSON 解析器进行填充。
Boost Json Translation (zh_Hans)/Doc / Pages / Comparison (adoc) — Chinese (Simplified Han script)
{icon_good} The fastest available JSON parser.
{icon_good} 为目前最快的JSON解析器。
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — English
= Allocation Control As <<ref_value_from>> creates a <<ref_value>> object, users may want to control the way memory is allocated for it. For this reason the function has an optional <<ref_storage_ptr>> parameter, that is used to set the {ref_memory_resource} for the result.
= Allocation Control As <<ref_value_from>> creates a <<ref_value>> object, users may want to control the way memory is allocated for it. For this reason the function has an optional <<ref_storage_ptr>> parameter, that is used to set the {ref_memory_resource} for the result.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — English
<<ref_value_to>> does not have a similar parameter, as <<ref_value>> is not created.
<<ref_value_to>> does not have a similar parameter, as <<ref_value>> is not created.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — English
As the conversion result is set via an output parameter of type `value&`, the intended <<ref_storage_ptr>> is correctly propagated. But users still should take care to not create temporaries using the default {ref_memory_resource} by accident.
As the conversion result is set via an output parameter of type `value&`, the intended <<ref_storage_ptr>> is correctly propagated. But users still should take care to not create temporaries using the default {ref_memory_resource} by accident.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — English
For example, consider this alternative implementation of `tag_invoke` for `ip_address` from the section <<custom_conversions>>.
For example, consider this alternative implementation of `tag_invoke` for `ip_address` from the section <<custom_conversions>>.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — English
``` void tag_invoke( const value_from_tag&, value& jv, ip_address const& addr ) { jv = array{ b[0], b[1], b[2], b[3] }; } ```
``` void tag_invoke( const value_from_tag&, value& jv, ip_address const& addr ) { jv = array{ b[0], b[1], b[2], b[3] }; } ```
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — English
This implementation explicitly creates an <<ref_array>> rather than relying on assignment from an initializer list. But the array uses default {ref_memory_resource}, not the one used by `jv`.
This implementation explicitly creates an <<ref_array>> rather than relying on assignment from an initializer list. But the array uses default {ref_memory_resource}, not the one used by `jv`.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — English
To avoid creating such temporaries with an incorrect {ref_memory_resource}, using <<ref_value>>'s member functions <<ref_value_emplace_array>>, <<ref_value_emplace_object>>, and <<ref_value_emplace_string>> can be helpful.
To avoid creating such temporaries with an incorrect {ref_memory_resource}, using <<ref_value>>'s member functions <<ref_value_emplace_array>>, <<ref_value_emplace_object>>, and <<ref_value_emplace_string>> can be helpful.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — Chinese (Simplified Han script)
= Allocation Control As <<ref_value_from>> creates a <<ref_value>> object, users may want to control the way memory is allocated for it. For this reason the function has an optional <<ref_storage_ptr>> parameter, that is used to set the {ref_memory_resource} for the result.
= 分配控制 由于&lt;<ref_value_from>&gt;会创建一个&lt;<ref_value>&gt;对象，用户可能希望控制其内存分配方式。因此，该函数具有一个可选的 &lt;<ref_storage_ptr>&gt; 参数，用于为结果指定{ref_memory_resource}。</ref_storage_ptr></ref_value></ref_value_from>
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — Chinese (Simplified Han script)
<<ref_value_to>> does not have a similar parameter, as <<ref_value>> is not created.
&lt;<ref_value_to>&gt; 没有类似的参数，因为该函数不会创建 &lt;<ref_value>&gt; 对象。</ref_value></ref_value_to>
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — Chinese (Simplified Han script)
As the conversion result is set via an output parameter of type `value&`, the intended <<ref_storage_ptr>> is correctly propagated. But users still should take care to not create temporaries using the default {ref_memory_resource} by accident.
由于转换结果是通过类型为`value&amp;`的输出参数设置的，因此预期的&lt;<ref_storage_ptr>&gt;会被正确传播。但用户仍需注意，避免意外创建使用默认 {ref_memory_resource} 的临时对象。</ref_storage_ptr>
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — Chinese (Simplified Han script)
For example, consider this alternative implementation of `tag_invoke` for `ip_address` from the section <<custom_conversions>>.
例如，考虑&lt;<custom_conversions>&gt;节中针对`ip_address`的`tag_invoke`的替代实现。</custom_conversions>
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — Chinese (Simplified Han script)
``` void tag_invoke( const value_from_tag&, value& jv, ip_address const& addr ) { jv = array{ b[0], b[1], b[2], b[3] }; } ```
``` void tag_invoke( const value_from_tag&amp;, value&amp; jv, ip_address const&amp; addr ) { jv = array{ b[0], b[1], b[2], b[3] }; } ```
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — Chinese (Simplified Han script)
This implementation explicitly creates an <<ref_array>> rather than relying on assignment from an initializer list. But the array uses default {ref_memory_resource}, not the one used by `jv`.
该实现显式创建了一个 &lt;<ref_array>&gt;，而不是依赖于初始化列表的赋值。但该数组使用的是默认的 {ref_memory_resource}，而不是`jv`所使用的内存资源。</ref_array>
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Alloc (adoc) — Chinese (Simplified Han script)
To avoid creating such temporaries with an incorrect {ref_memory_resource}, using <<ref_value>>'s member functions <<ref_value_emplace_array>>, <<ref_value_emplace_object>>, and <<ref_value_emplace_string>> can be helpful.
为避免创建使用错误 {ref_memory_resource} 的临时对象，可以借助 &lt;<ref_value>&gt; 的成员函数 &lt;<ref_value_emplace_array>&gt;、&lt;<ref_value_emplace_object>&gt; 和 &lt;<ref_value_emplace_string>&gt;。</ref_value_emplace_string></ref_value_emplace_object></ref_value_emplace_array></ref_value>
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Context (adoc) — English
= Contextual Conversions Previously in this section we've been assuming that there is a particular fitting JSON representation for a type. But this is not always the case. Often one needs to represent particular value with JSON of certain format in one situation and with another format in a different situation. This can be achieved with Boost.JSON by providing an extra argument---context.
= Contextual Conversions Previously in this section we've been assuming that there is a particular fitting JSON representation for a type. But this is not always the case. Often one needs to represent particular value with JSON of certain format in one situation and with another format in a different situation. This can be achieved with Boost.JSON by providing an extra argument---context.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Context (adoc) — English
Let's implement conversion from `user_ns::ip_address` to a JSON string:
Let's implement conversion from `user_ns::ip_address` to a JSON string:
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Context (adoc) — English
These `tag_invoke` overloads take an extra `as_string` parameter, which disambiguates this specific representation of `ip_address` from all other potential representations. In order to take advantage of them one needs to pass an `as_string` object to <<ref_value_from>> or <<ref_value_to>> as the last argument:
These `tag_invoke` overloads take an extra `as_string` parameter, which disambiguates this specific representation of `ip_address` from all other potential representations. In order to take advantage of them one needs to pass an `as_string` object to <<ref_value_from>> or <<ref_value_to>> as the last argument:
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Context (adoc) — English
Note, that if there is no dedicated `tag_invoke` overload for a given type and a given context, the implementation falls back to overloads without context. Thus it is easy to combine contextual conversions with conversions provided by the library:
Note, that if there is no dedicated `tag_invoke` overload for a given type and a given context, the implementation falls back to overloads without context. Thus it is easy to combine contextual conversions with conversions provided by the library:
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Context (adoc) — English
Conversions for Third-Party Types
Conversions for Third-Party Types
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Context (adoc) — English
Normally, you wouldn't be able to provide conversions for types from third-party libraries and standard types, because it would require yout to put `tag_invoke` overloads into namespaces you do not control. But with contexts you can put the overloads into your namespaces. This is because the context will add its associated namespaces into the list of namespaces where `tag_invoke` overloads are searched.
Normally, you wouldn't be able to provide conversions for types from third-party libraries and standard types, because it would require yout to put `tag_invoke` overloads into namespaces you do not control. But with contexts you can put the overloads into your namespaces. This is because the context will add its associated namespaces into the list of namespaces where `tag_invoke` overloads are searched.
Boost Json Translation (zh_Hans)/Doc / Pages / Conversion / Context (adoc) — English
As an example, let's implement conversion for https://en.cppreference.com/w/cpp/chrono/system_clock[``std::chrono::system_clock::time_point``s] using https://en.wikipedia.org/wiki/ISO_8601[ISO 8601] format.
As an example, let's implement conversion for https://en.cppreference.com/w/cpp/chrono/system_clock[``std::chrono::system_clock::time_point``s] using https://en.wikipedia.org/wiki/ISO_8601[ISO 8601] format.
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Reverse conversion is left out for brevity.
Reverse conversion is left out for brevity.
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The new context is used in a similar fashion to `as_string` previously in this section.
The new context is used in a similar fashion to `as_string` previously in this section.
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One particular use case that is enabled by contexts is adaptor libraries that define JSON conversion logic for types from a different library.
One particular use case that is enabled by contexts is adaptor libraries that define JSON conversion logic for types from a different library.
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Passing Data to Conversion Functions
Passing Data to Conversion Functions
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Contexts we used so far were empty classes. But contexts may have data members and member functions just as any class. Implementers of conversion functions can take advantage of that to have conversions configurable at runtime or pass special objects to conversions (e.g. allocators).
Contexts we used so far were empty classes. But contexts may have data members and member functions just as any class. Implementers of conversion functions can take advantage of that to have conversions configurable at runtime or pass special objects to conversions (e.g. allocators).
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Let's rewrite conversion for ``system_clock::time_point``s to allow any format supported by `std::strftime`.
Let's rewrite conversion for ``system_clock::time_point``s to allow any format supported by `std::strftime`.
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This `tag_invoke` overload lets us change date conversion format at runtime. Also note, that there is no ambiguity between `as_iso_8601` overload and `date_format` overload. You can use both in your program:
This `tag_invoke` overload lets us change date conversion format at runtime. Also note, that there is no ambiguity between `as_iso_8601` overload and `date_format` overload. You can use both in your program:
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Combining Contexts
Combining Contexts
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Often it is needed to use several conversion contexts together. For example, consider a log of remote users identified by IP addresses accessing a system. We can represent it as `std::vector<std::pair<std::chrono::system_clock::time_point, ip_address>>`. We want to serialize both ``ip_address``es and ``time_point``s as strings, but for this we need both `as_string` and `as_iso_8601` contexts. To combine several contexts just use {std_tuple}. Conversion functions will select the first element of the tuple for which a `tag_invoke` overload exists and will call that overload. As usual, `tag_invoke` overloads that don't use contexts and library-provided generic conversions are also supported. Thus, here's our example:
Often it is needed to use several conversion contexts together. For example, consider a log of remote users identified by IP addresses accessing a system. We can represent it as `std::vector<std::pair<std::chrono::system_clock::time_point, ip_address>>`. We want to serialize both ``ip_address``es and ``time_point``s as strings, but for this we need both `as_string` and `as_iso_8601` contexts. To combine several contexts just use {std_tuple}. Conversion functions will select the first element of the tuple for which a `tag_invoke` overload exists and will call that overload. As usual, `tag_invoke` overloads that don't use contexts and library-provided generic conversions are also supported. Thus, here's our example:
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In this snippet `time_point` is converted using `tag_invoke` overload that takes `as_iso_8601`, `ip_address` is converted using `tag_invoke` overload that takes `as_string`, and {std_vector} is converted using a generic conversion provided by the library.
In this snippet `time_point` is converted using `tag_invoke` overload that takes `as_iso_8601`, `ip_address` is converted using `tag_invoke` overload that takes `as_string`, and {std_vector} is converted using a generic conversion provided by the library.
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Contexts and Composite Types
Contexts and Composite Types
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As was shown previously, generic conversions provided by the library forward contexts to conversions of nested objects. And in the case when you want to provide your own conversion function for a composite type enabled by a particular context, you usually also need to do that.
As was shown previously, generic conversions provided by the library forward contexts to conversions of nested objects. And in the case when you want to provide your own conversion function for a composite type enabled by a particular context, you usually also need to do that.
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Consider this example. As was discussed in a previous section, <<ref_is_map_like>> requires that your key type satisfies <<ref_is_string_like>>. Now, let's say your keys are not string-like, but they do convert to <<ref_string>>. You can make such maps to also convert to objects using a context. But if you want to also use another context for values, you need a way to pass the full combined context to map elements. So, you want the following test to succeed.
Consider this example. As was discussed in a previous section, <<ref_is_map_like>> requires that your key type satisfies <<ref_is_string_like>>. Now, let's say your keys are not string-like, but they do convert to <<ref_string>>. You can make such maps to also convert to objects using a context. But if you want to also use another context for values, you need a way to pass the full combined context to map elements. So, you want the following test to succeed.