= Numbers JSON numbers are represented using `std::int64_t`, `std::uint64_t`, and `double`. When a <<ref_value>> is constructed from an unsigned integer, its <<ref_kind>> will be `kind::uint64`. Likewise, a <<ref_value>> constructed from a signed integer will have `kind::int64`, or `kind::double_` if constructed from a floating-point type:

When accessing a number contained within a <<ref_value>>, the function used must match the value's <<ref_kind>> exactly; no conversions will be performed. For example if `as_double` is called on a <<ref_value>> that contains a `std::uint64_t`, an exception is thrown. Similarly, the function `if_double` will return `nullptr` and calling `get_double` will result in undefined behavior:

In cases where you know that a <<ref_value>> contains a number but don't know its <<ref_kind>>, `value::to_number` can be used to convert the <<ref_value>> to an arithmetic type:

If the <<ref_value>> does not contain a number, or if the conversion is to an integer type `T` and the number cannot be represented exactly by `T`, the conversion will fail. Otherwise, the result is the number converted to `T` as-if by `static_cast`: