[#nlohmann-basic_json-0e-2conversion-03]
= xref:nlohmann.adoc[nlohmann]::xref:nlohmann/basic_json-0e.adoc[basic_json<>]::operator ValueType
:relfileprefix: ../../
:mrdocs:

get a value (implicit)

== Synopsis

Declared in `<nlohmann/json.hpp>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<typename ValueType>
requires detail::conjunction <
                       detail::negation<std::is_pointer<ValueType>>,
                       detail::negation<std::is_same<ValueType, std::nullptr_t>>,
                       detail::negation<std::is_same<ValueType, detail::json_ref<basic_json>>>,
                                        detail::negation<std::is_same<ValueType, typename string_t::value_type>>,
                                        detail::negation<detail::is_basic_json<ValueType>>,
                                        detail::negation<std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>>,
#if defined(JSON_HAS_CPP_17) && (defined(__GNUC__) || (defined(_MSC_VER) && _MSC_VER >= 1910 && _MSC_VER <= 1914))
                                                detail::negation<std::is_same<ValueType, std::string_view>>,
#endif
#if defined(JSON_HAS_CPP_17) && JSON_HAS_STATIC_RTTI
                                                detail::negation<std::is_same<ValueType, std::any>>,
#endif
                                                detail::is_detected_lazy<detail::get_template_function, const basic_json_t&, ValueType>
                                                >::value
operator ValueType() const;
----

== Description

Implicit type conversion between the JSON value and a compatible value. The call is realized by calling xref:nlohmann/basic_json-0e/get-01.adoc[`get() const`].

Linear in the size of the JSON value.

{The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating‐point numbers can be converted to integers, (2) A JSON array can be converted to a standard `std::vector<short>`, (3) A JSON object can be converted to C++ associative containers such as `std::unordered_map<std::string, json>`.,operator_ValueType}

== Exceptions

[cols=2]
|===
| Name
| Thrown on
| `type_error.302`
| in case passed type _ValueType_ is incompatible to the JSON value type (e.g., the JSON value is of type boolean, but a string is requested); see example below
|===

== Return Value

copy of the JSON value, converted to type _ValueType_

== Template Parameters

[cols=2]
|===
| Name
| Description
| *ValueType*
| non‐pointer type compatible to the JSON value, for instance `int` for JSON integer numbers, `bool` for JSON booleans, or `std::vector` types for JSON arrays. The character type of xref:nlohmann/basic_json-0e/string_t.adoc[`string_t`] as well as an initializer list of this type is excluded to avoid ambiguities as these types implicitly convert to `std::string`.
|===


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