Exit Zen
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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.
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For this you will have to use a different overload of `tag_invoke`. This time it has to be a function template, and it should have two parameters for contexts. The first parameter is the specific context that disambiguates that particular overload. The second parameter is the full context passed to <<ref_value_to>> or <<ref_value_from>>.
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The <<ref_parse>> function offers a simple interface for converting a serialized JSON text to a <<ref_value>> in a single function call. This overload uses exceptions to indicate errors:
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Simple free functions are provided for serializing a <<ref_value>> to a {std_string} containing JSON:
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{icon_bad} Object types have no hash table or index to reduce the cost of
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are replaced with an overload accepting a <<ref_string_view>> parameter.
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Boost.JSON solves this problem by introducing a new smart pointer called <<ref_storage_ptr>> which builds upon {cpp}17's memory allocation interfaces, accomplishing the goals above. As a result, libraries which use this type compose more easily and enjoy faster compilation, as member functions for containers which use the type can be defined out-of-line.
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lookups.
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Type satisfying <<ref_is_string_like>>.
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This design removes several redundant overloads from the interface. For example, the 11 overloads of `std::string::insert` are reduced to just 3 in <<ref_string>>, while still providing identical functionality. In addition to these changes, overloads taking a `std::initializer_list<char>` parameter have been removed. Such overloads have little use, as they serve as little more than wrappers for arrays with an inefficient syntax:
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The <<ref_value>> returned in the preceding examples use the <<default_memory_resource,default memory resource>>. The following code uses a <<ref_monotonic_resource>>, which results in faster parsing. `jv` is marked `const` to prevent subsequent modification, because containers using a monotonic resource waste memory when mutated.
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{icon_bad} Allocators have reference semantics. Problems with lifetime are
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With the removal of overloads that specify parameters for a substring, a member function `subview` that returns a <<ref_string_view>> is provided to facilitate cheap substring operations:
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We can define a conversion from the user-defined type to a <<ref_value>> by defining an overload of `tag_invoke` in the same namespace. This maps `customer` to a JSON object:
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easily encountered.
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The result is a <<ref_string>>.
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A <<ref_string>> may be constructed using the <<default_memory_resource,default memory resource>> without incurring any memory allocations. Alternatively, a <<ref_storage_ptr>> can be provided explicitly:
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Unless otherwise specified, the parser in this library is strict. It recognizes only valid, standard JSON. The parser can be configured to allow certain non-standard extensions by filling in a <<ref_parse_options>> structure and passing it by value. By default all extensions are disabled:
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This allows us to use the library function <<ref_value_from>> to produce a <<ref_value>> from our type:
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The result is constructed from a <<ref_string_view>>.
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