Exit Zen
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The emplace members of <<ref_value>> return a typed reference to the underlying representation. For example, the call to <<ref_value_emplace_string,`value::emplace_string`>> in the previous example returns a <<ref_string,`string&`>>. This table shows the underlying type for each kind:
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interface similar to {std_unordered_map}, that remembers insertion order.
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`std::int64_t`
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`std::uint64_t`
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`double`
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https://en.cppreference.com/w/cpp/keyword/bool[`bool`]
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If the <<ref_kind>> of a <<ref_value>> is known, functions such as <<ref_value_as_bool,`value::as_bool`>> or <<ref_value_as_string,`value::as_string`>> may be used to obtain a reference to the underlying representation without changing the existing value:
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However, as shown above these functions throw an exception if the kind in the <<ref_value>> does not match the kind denoted by the function signature. This can be used as a concise form of validation: access values as if they were the right type, but handle the resulting exception indicating if the schema of the JSON is not valid.
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We can query a value for its underlying representation of a particular kind in a way that does not throw exceptions by requesting a pointer which may be null, instead of a reference. Here we use <<ref_value_if_string,`value::if_string`>> to conditionally perform an assignment without using exceptions:
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When a <<ref_value>> is formatted to a {std_ostream}, the result is serialized JSON as if by calling <<ref_serialize>>.
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