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	= Custom Conversions Boost.JSON uses two mechanisms to customize conversion between <<ref_value>> and user types. One mechanism involves specializing type traits. The other one is more powerful and requires defining overloads of `tag_invoke`. Both mechanisms will be further explained in this section.	= 自定义转换 Boost.JSON 提供了两种机制用于自定义 <<ref_value>> 与用户类型之间的转换。一种机制涉及特化类型特征（type traits）。另一种机制更强大，需要定义`tag_invoke`的重载。本节将进一步解释这两种机制。</ref_value>
	Conversion Traits	转换特征
	Previously a number of conversion type traits, like <<ref_is_tuple_like>> or <<ref_is_sequence_like>>, were introduced. The library tries the traits one after another and uses the implementation that corresponds to the first matching trait. In some cases, though, a type would match a trait with a higher priority, but the user intends for it to belong to a lower priority category. If this happens the user can specialize the trait that's not supposed to match for that type to be an equivalent of `std::false_type`.	之前已经介绍了一些转换类型特征，例如 <<ref_is_tuple_like>> 或 <<ref_is_sequence_like>>。库会依次尝试这些特征，并使用与第一个匹配特征对应的实现。然而，在某些情况下，某个类型可能会匹配到优先级更高的特征，而用户实际希望将其归入优先级更低的类别。如果发生这种情况，用户可以针对该类型特化那个不应匹配的特征，使其等同于`std::false_type`。</ref_is_sequence_like></ref_is_tuple_like>
	Consider this type:	考虑以下类型：
	It exposes both a sequence API and a tuple API. But converting from <<ref_value>> to `user_ns::ip_address` would not be able to use implementation for sequences, since those are constructed empty and then populated one element at a time, while `ip_address` has a fixed size of 4. The tuple conversion would fit, though. The only problem is that <<ref_is_tuple_like>> has a lower priority than <<ref_is_sequence_like>>. In order to circumvent this, the user only needs to specialize <<ref_is_sequence_like>> to not match `ip_address`.	它同时暴露了序列（sequence）API 和元组（tuple）API。然而，从 <<ref_value>> 转换到 user_ns::ip_address 时无法使用序列的实现，因为序列类型的转换会先构造一个空对象，再逐个填充元素，而 ip_address 的大小固定为 4。相比之下，元组转换是合适的。唯一的问题在于 <<ref_is_tuple_like>> 的优先级低于 <<ref_is_sequence_like>>。为绕过此问题，用户只需特化 <<ref_is_sequence_like>>，使其对 ip_address 不匹配即可。</ref_is_sequence_like></ref_is_sequence_like></ref_is_tuple_like></ref_value>
	`tag_invoke` Overloads	`tag_invoke`重载
	The second, more powerful approach, is to provide the conversion implementation yourself. With Boost.JSON this is done by defining an overload of `tag_invoke` function (the benefits of this mechanism are outlined in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf[C++ proposal P1895]. In essence, `tag_invoke` provides a uniform interface for defining customization points by using argument-dependent lookup to find a viable overload from the point at which it is called. As the name suggests, a tag type is passed as an argument in order to:	第二种、更强大的方法是自行提供转换实现。在 Boost.JSON 中，这是通过定义`tag_invoke`函数的重载来实现的（该机制的优点详见 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf[C++提案P1895]）。本质上，`tag_invoke` 通过参数依赖查找（ADL）在调用点寻找可用的重载，从而为自定义扩展点提供统一接口。顾名思义，一个标签类型作为参数传递，用于：
	discard candidates that are unrelated to that particular	排除与该特定自定义点无关的候选函数，
	customization point, and	并且
	embed the user-defined type into the arguments list (e.g. by using a tag type	将用户自定义类型嵌入到参数列表中（例如，通过使用
	template such as `value_to_tag<T>`) so that its http://eel.is/c++draft/basic.lookup.argdep#2[associated namespaces and entities] are examined when name lookup is performed.	像`value_to_tag<t>`这样的标签类型模板），以便在执行名称查找时检查其http://eel.is/c++draft/basic.lookup.argdep#2[关联的命名空间和实体]。</t>
	This has the effect of finding user-provided `tag_invoke` overloads, even if they are declared (lexically) after the definition of the calling function.	这能够识别用户提供的`tag_invoke`重载函数，即便这些重载函数是（从词法角度来看）在调用函数的定义之后声明的。
	Overloads of `tag_invoke` called by <<ref_value_from>> take the form:	由 <<ref_value_from>> 调用的 `tag_invoke` 的重载形式如下：</ref_value_from>
	``` void tag_invoke( const value_from_tag&, value&, T ); ```	``` void tag_invoke( const value_from_tag&, value&, T ); ```
	While overloads of `tag_invoke` called by <<ref_value_to>> take the form:	而由 <<ref_value_to>> 调用的`tag_invoke`重载采用以下形式：</ref_value_to>
	``` T tag_invoke( const value_to_tag< T >&, const value& ); ```	``` T tag_invoke( const value_to_tag< T >&, const value& ); ```

	English	Chinese (Simplified Han script)	Actions
	Overloads of `tag_invoke` called by <<ref_value_from>> take the form:	由 <<ref_value_from>> 调用的 `tag_invoke` 的重载形式如下：</ref_value_from>
	Conversion Traits	转换特征
	= Custom Conversions Boost.JSON uses two mechanisms to customize conversion between <<ref_value>> and user types. One mechanism involves specializing type traits. The other one is more powerful and requires defining overloads of `tag_invoke`. Both mechanisms will be further explained in this section.	= 自定义转换 Boost.JSON 提供了两种机制用于自定义 <<ref_value>> 与用户类型之间的转换。一种机制涉及特化类型特征（type traits）。另一种机制更强大，需要定义`tag_invoke`的重载。本节将进一步解释这两种机制。</ref_value>
	embed the user-defined type into the arguments list (e.g. by using a tag type	将用户自定义类型嵌入到参数列表中（例如，通过使用
	Previously a number of conversion type traits, like <<ref_is_tuple_like>> or <<ref_is_sequence_like>>, were introduced. The library tries the traits one after another and uses the implementation that corresponds to the first matching trait. In some cases, though, a type would match a trait with a higher priority, but the user intends for it to belong to a lower priority category. If this happens the user can specialize the trait that's not supposed to match for that type to be an equivalent of `std::false_type`.	之前已经介绍了一些转换类型特征，例如 <<ref_is_tuple_like>> 或 <<ref_is_sequence_like>>。库会依次尝试这些特征，并使用与第一个匹配特征对应的实现。然而，在某些情况下，某个类型可能会匹配到优先级更高的特征，而用户实际希望将其归入优先级更低的类别。如果发生这种情况，用户可以针对该类型特化那个不应匹配的特征，使其等同于`std::false_type`。</ref_is_sequence_like></ref_is_tuple_like>
	Consider this type:	考虑以下类型：
	It exposes both a sequence API and a tuple API. But converting from <<ref_value>> to `user_ns::ip_address` would not be able to use implementation for sequences, since those are constructed empty and then populated one element at a time, while `ip_address` has a fixed size of 4. The tuple conversion would fit, though. The only problem is that <<ref_is_tuple_like>> has a lower priority than <<ref_is_sequence_like>>. In order to circumvent this, the user only needs to specialize <<ref_is_sequence_like>> to not match `ip_address`.	它同时暴露了序列（sequence）API 和元组（tuple）API。然而，从 <<ref_value>> 转换到 user_ns::ip_address 时无法使用序列的实现，因为序列类型的转换会先构造一个空对象，再逐个填充元素，而 ip_address 的大小固定为 4。相比之下，元组转换是合适的。唯一的问题在于 <<ref_is_tuple_like>> 的优先级低于 <<ref_is_sequence_like>>。为绕过此问题，用户只需特化 <<ref_is_sequence_like>>，使其对 ip_address 不匹配即可。</ref_is_sequence_like></ref_is_sequence_like></ref_is_tuple_like></ref_value>
	`tag_invoke` Overloads	`tag_invoke`重载
	The second, more powerful approach, is to provide the conversion implementation yourself. With Boost.JSON this is done by defining an overload of `tag_invoke` function (the benefits of this mechanism are outlined in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf[C++ proposal P1895]. In essence, `tag_invoke` provides a uniform interface for defining customization points by using argument-dependent lookup to find a viable overload from the point at which it is called. As the name suggests, a tag type is passed as an argument in order to:	第二种、更强大的方法是自行提供转换实现。在 Boost.JSON 中，这是通过定义`tag_invoke`函数的重载来实现的（该机制的优点详见 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf[C++提案P1895]）。本质上，`tag_invoke` 通过参数依赖查找（ADL）在调用点寻找可用的重载，从而为自定义扩展点提供统一接口。顾名思义，一个标签类型作为参数传递，用于：
	discard candidates that are unrelated to that particular	排除与该特定自定义点无关的候选函数，
	customization point, and	并且
	template such as `value_to_tag<T>`) so that its http://eel.is/c++draft/basic.lookup.argdep#2[associated namespaces and entities] are examined when name lookup is performed.	像`value_to_tag<t>`这样的标签类型模板），以便在执行名称查找时检查其http://eel.is/c++draft/basic.lookup.argdep#2[关联的命名空间和实体]。</t>
	This has the effect of finding user-provided `tag_invoke` overloads, even if they are declared (lexically) after the definition of the calling function.	这能够识别用户提供的`tag_invoke`重载函数，即便这些重载函数是（从词法角度来看）在调用函数的定义之后声明的。
	``` void tag_invoke( const value_from_tag&, value&, T ); ```	``` void tag_invoke( const value_from_tag&, value&, T ); ```
	While overloads of `tag_invoke` called by <<ref_value_to>> take the form:	而由 <<ref_value_to>> 调用的`tag_invoke`重载采用以下形式：</ref_value_to>
	``` T tag_invoke( const value_to_tag< T >&, const value& ); ```	``` T tag_invoke( const value_to_tag< T >&, const value& ); ```
	If we implemented conversion for `user_ns::ip_address` manually with this approach, it would look like this:	如果我们采用这种方式手动对 `user_ns::ip_address` 进行转换，其效果将会是这样的：

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= Custom Conversions Boost.JSON uses two mechanisms to customize conversion between <<ref_value>> and user types. One mechanism involves specializing type traits. The other one is more powerful and requires defining overloads of `tag_invoke`. Both mechanisms will be further explained in this section.自定义转换 Boost.JSON 提供了两种机制用于自定义 <<ref_value>> 与用户类型之间的转换。一种机制涉及特化类型特征（type traits）。另一种机制更强大，需要定义`tag_invoke`的重载。本节将进一步解释这两种机制。</ref_value>

06/05/2026

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Chinese (Simplified Han script) 301 characters editedPrevious translationState: Needs editing (Needs rewriting)

06/05/2026

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doc/pages/conversion/custom_zh_Hans.adoc, string 1

Shortcut	Action
`?`	Open available keyboard shortcuts.
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