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* Copyright 2011-present Facebook, Inc.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
* This is a runtime dynamically typed value. It holds types from a
* specific predetermined set of types (ints, bools, arrays, etc). In
* particular, it can be used as a convenient in-memory representation
* for complete json objects.
* In general you can try to use these objects as if they were the
* type they represent (although in some cases with a slightly less
* complete interface than the raw type), and it'll just throw a
* TypeError if it is used in an illegal way.
* Some examples:
* dynamic twelve = 12;
* dynamic str = "string";
* dynamic map = dynamic::object;
* map[str] = twelve;
* map[str + "another_str"] = dynamic::array("array", "of", 4, "elements");
* map.insert("null_element", nullptr);
* ++map[str];
* assert(map[str] == 13);
* // Building a complex object with a sub array inline:
* dynamic d = dynamic::object
* ("key", "value")
* ("key2", dynamic::array("a", "array"))
* ;
* Also see folly/json.h for the serialization and deserialization
* functions for JSON.
* Additional documentation is in folly/docs/
* @author Jordan DeLong <>
#pragma once
#include <cstdint>
#include <memory>
#include <ostream>
#include <string>
#include <type_traits>
#include <unordered_map>
#include <utility>
#include <vector>
#include <boost/operators.hpp>
#include <folly/Range.h>
#include <folly/Traits.h>
#include <folly/json_pointer.h>
namespace folly {
struct dynamic;
struct TypeError;
struct dynamic : private boost::operators<dynamic> {
enum Type {
template <class T, class Enable = void> struct NumericTypeHelper;
* We support direct iteration of arrays, and indirect iteration of objects.
* See begin(), end(), keys(), values(), and items() for more.
* Array iterators dereference as the elements in the array.
* Object key iterators dereference as the keys in the object.
* Object value iterators dereference as the values in the object.
* Object item iterators dereference as pairs of (key, value).
typedef std::vector<dynamic> Array;
typedef Array::iterator iterator;
typedef Array::const_iterator const_iterator;
typedef dynamic value_type;
struct const_key_iterator;
struct const_value_iterator;
struct const_item_iterator;
struct value_iterator;
struct item_iterator;
* Creation routines for making dynamic objects and arrays. Objects
* are maps from key to value (so named due to json-related origins
* here).
* Example:
* // Make a fairly complex dynamic:
* dynamic d = dynamic::object("key", "value1")
* ("key2", dynamic::array("value",
* "with",
* 4,
* "words"));
* // Build an object in a few steps:
* dynamic d = dynamic::object;
* d["key"] = 12;
* d["something_else"] = dynamic::array(1, 2, 3, nullptr);
struct EmptyArrayTag {};
struct ObjectMaker;
static void array(EmptyArrayTag);
template <class... Args>
static dynamic array(Args&& ...args);
static ObjectMaker object();
static ObjectMaker object(dynamic, dynamic);
* Default constructor, initializes with nullptr.
* String compatibility constructors.
/* implicit */ dynamic(std::nullptr_t);
/* implicit */ dynamic(StringPiece val);
/* implicit */ dynamic(char const* val);
/* implicit */ dynamic(std::string val);
* This is part of the plumbing for array() and object(), above.
* Used to create a new array or object dynamic.
/* implicit */ dynamic(void (*)(EmptyArrayTag));
/* implicit */ dynamic(ObjectMaker (*)());
/* implicit */ dynamic(ObjectMaker const&) = delete;
/* implicit */ dynamic(ObjectMaker&&);
* Constructors for integral and float types.
* Other types are SFINAEd out with NumericTypeHelper.
template <class T, class NumericType = typename NumericTypeHelper<T>::type>
/* implicit */ dynamic(T t);
* Create a dynamic that is an array of the values from the supplied
* iterator range.
template <class Iterator>
explicit dynamic(Iterator first, Iterator last);
dynamic(dynamic const&);
dynamic(dynamic&&) noexcept;
~dynamic() noexcept;
* "Deep" equality comparison. This will compare all the way down
* an object or array, and is potentially expensive.
bool operator==(dynamic const& o) const;
* For all types except object this returns the natural ordering on
* those types. For objects, we throw TypeError.
bool operator<(dynamic const& o) const;
* General operators.
* These throw TypeError when used with types or type combinations
* that don't support them.
* These functions may also throw if you use 64-bit integers with
* doubles when the integers are too big to fit in a double.
dynamic& operator+=(dynamic const&);
dynamic& operator-=(dynamic const&);
dynamic& operator*=(dynamic const&);
dynamic& operator/=(dynamic const&);
dynamic& operator%=(dynamic const&);
dynamic& operator|=(dynamic const&);
dynamic& operator&=(dynamic const&);
dynamic& operator^=(dynamic const&);
dynamic& operator++();
dynamic& operator--();
* Assignment from other dynamics. Because of the implicit conversion
* to dynamic from its potential types, you can use this to change the
* type pretty intuitively.
* Basic guarantee only.
dynamic& operator=(dynamic const&);
dynamic& operator=(dynamic&&) noexcept;
* For simple dynamics (not arrays or objects), this prints the
* value to an std::ostream in the expected way. Respects the
* formatting manipulators that have been sent to the stream
* already.
* If the dynamic holds an object or array, this prints them in a
* format very similar to JSON. (It will in fact actually be JSON
* as long as the dynamic validly represents a JSON object---i.e. it
* can't have non-string keys.)
friend std::ostream& operator<<(std::ostream&, dynamic const&);
* Returns true if this dynamic is of the specified type.
bool isString() const;
bool isObject() const;
bool isBool() const;
bool isNull() const;
bool isArray() const;
bool isDouble() const;
bool isInt() const;
* Returns: isInt() || isDouble().
bool isNumber() const;
* Returns the type of this dynamic.
Type type() const;
* Returns the type of this dynamic as a printable string.
const char* typeName() const;
* Extract a value while trying to convert to the specified type.
* Throws exceptions if we cannot convert from the real type to the
* requested type.
* Note you can only use this to access integral types or strings,
* since arrays and objects are generally best dealt with as a
* dynamic.
std::string asString() const;
double asDouble() const;
int64_t asInt() const;
bool asBool() const;
* Extract the value stored in this dynamic without type conversion.
* These will throw a TypeError if the dynamic has a different type.
const std::string& getString() const&;
double getDouble() const&;
int64_t getInt() const&;
bool getBool() const&;
std::string& getString() &;
double& getDouble() &;
int64_t& getInt() &;
bool& getBool() &;
std::string&& getString() &&;
double getDouble() &&;
int64_t getInt() &&;
bool getBool() &&;
* It is occasionally useful to access a string's internal pointer
* directly, without the type conversion of `asString()`.
* These will throw a TypeError if the dynamic is not a string.
const char* data() const&;
const char* data() && = delete;
const char* c_str() const&;
const char* c_str() && = delete;
StringPiece stringPiece() const;
* Returns: true if this dynamic is null, an empty array, an empty
* object, or an empty string.
bool empty() const;
* If this is an array or an object, returns the number of elements
* contained. If it is a string, returns the length. Otherwise
* throws TypeError.
std::size_t size() const;
* You can iterate over the values of the array. Calling these on
* non-arrays will throw a TypeError.
const_iterator begin() const;
const_iterator end() const;
iterator begin();
iterator end();
* Helper object returned by keys(), values(), and items().
template <class T> struct IterableProxy;
* You can iterate over the keys, values, or items (std::pair of key and
* value) in an object. Calling these on non-objects will throw a TypeError.
IterableProxy<const_key_iterator> keys() const;
IterableProxy<const_value_iterator> values() const;
IterableProxy<const_item_iterator> items() const;
IterableProxy<value_iterator> values();
IterableProxy<item_iterator> items();
* AssociativeContainer-style find interface for objects. Throws if
* this is not an object.
* Returns: items().end() if the key is not present, or a
* const_item_iterator pointing to the item.
const_item_iterator find(dynamic const&) const;
item_iterator find(dynamic const&);
* If this is an object, returns whether it contains a field with
* the given name. Otherwise throws TypeError.
std::size_t count(dynamic const&) const;
* For objects or arrays, provides access to sub-fields by index or
* field name.
* Using these with dynamic objects that are not arrays or objects
* will throw a TypeError. Using an index that is out of range or
* object-element that's not present throws std::out_of_range.
dynamic const& at(dynamic const&) const&;
dynamic& at(dynamic const&) &;
dynamic&& at(dynamic const&) &&;
* Locate element using JSON pointer, per RFC 6901. Returns nullptr if
* element could not be located. Throws if pointer does not match the
* shape of the document, e.g. uses string to index in array.
const dynamic* get_ptr(json_pointer const&) const&;
dynamic* get_ptr(json_pointer const&) &;
const dynamic* get_ptr(json_pointer const&) const&& = delete;
dynamic* get_ptr(json_pointer const&) && = delete;
* Like 'at', above, except it returns either a pointer to the contained
* object or nullptr if it wasn't found. This allows a key to be tested for
* containment and retrieved in one operation. Example:
* if (auto* found = d.get_ptr(key))
* // use *found;
* Using these with dynamic objects that are not arrays or objects
* will throw a TypeError.
const dynamic* get_ptr(dynamic const&) const&;
dynamic* get_ptr(dynamic const&) &;
dynamic* get_ptr(dynamic const&) && = delete;
* This works for access to both objects and arrays.
* In the case of an array, the index must be an integer, and this
* will throw std::out_of_range if it is less than zero or greater
* than size().
* In the case of an object, the non-const overload inserts a null
* value if the key isn't present. The const overload will throw
* std::out_of_range if the key is not present.
* These functions do not invalidate iterators except when a null value
* is inserted into an object as described above.
dynamic& operator[](dynamic const&) &;
dynamic const& operator[](dynamic const&) const&;
dynamic&& operator[](dynamic const&) &&;
* Only defined for objects, throws TypeError otherwise.
* getDefault will return the value associated with the supplied key, the
* supplied default otherwise. setDefault will set the key to the supplied
* default if it is not yet set, otherwise leaving it. setDefault returns
* a reference to the existing value if present, the new value otherwise.
getDefault(const dynamic& k, const dynamic& v = dynamic::object) const&;
dynamic getDefault(const dynamic& k, dynamic&& v) const&;
dynamic getDefault(const dynamic& k, const dynamic& v = dynamic::object) &&;
dynamic getDefault(const dynamic& k, dynamic&& v) &&;
template <class K, class V>
dynamic& setDefault(K&& k, V&& v);
// MSVC 2015 Update 3 needs these extra overloads because if V were a
// defaulted template parameter, it causes MSVC to consider v an rvalue
// reference rather than a universal reference, resulting in it not being
// able to find the correct overload to construct a dynamic with.
template <class K>
dynamic& setDefault(K&& k, dynamic&& v);
template <class K>
dynamic& setDefault(K&& k, const dynamic& v = dynamic::object);
* Resizes an array so it has at n elements, using the supplied
* default to fill new elements. Throws TypeError if this dynamic
* is not an array.
* May invalidate iterators.
* Post: size() == n
void resize(std::size_t n, dynamic const& = nullptr);
* Inserts the supplied key-value pair to an object, or throws if
* it's not an object.
* Invalidates iterators.
template <class K, class V> void insert(K&&, V&& val);
* These functions merge two folly dynamic objects.
* The "update" and "update_missing" functions extend the object by
* inserting the key/value pairs of mergeObj into the current object.
* For update, if key is duplicated between the two objects, it
* will overwrite with the value of the object being inserted (mergeObj).
* For "update_missing", it will prefer the value in the original object
* The "merge" function creates a new object consisting of the key/value
* pairs of both mergeObj1 and mergeObj2
* If the key is duplicated between the two objects,
* it will prefer value in the second object (mergeObj2)
void update(const dynamic& mergeObj);
void update_missing(const dynamic& other);
static dynamic merge(const dynamic& mergeObj1, const dynamic& mergeObj2);
* Implement recursive version of RFC7386: JSON merge patch. This modifies
* the current object.
void merge_patch(const dynamic& patch);
* Computes JSON merge patch (RFC7386) needed to mutate from source to target
static dynamic merge_diff(const dynamic& source, const dynamic& target);
* Erase an element from a dynamic object, by key.
* Invalidates iterators to the element being erased.
* Returns the number of elements erased (i.e. 1 or 0).
std::size_t erase(dynamic const& key);
* Erase an element from a dynamic object or array, using an
* iterator or an iterator range.
* In arrays, invalidates iterators to elements after the element
* being erased. In objects, invalidates iterators to the elements
* being erased.
* Returns a new iterator to the first element beyond any elements
* removed, or end() if there are none. (The iteration order does
* not change.)
iterator erase(const_iterator it);
iterator erase(const_iterator first, const_iterator last);
const_key_iterator erase(const_key_iterator it);
const_key_iterator erase(const_key_iterator first, const_key_iterator last);
value_iterator erase(const_value_iterator it);
value_iterator erase(const_value_iterator first, const_value_iterator last);
item_iterator erase(const_item_iterator it);
item_iterator erase(const_item_iterator first, const_item_iterator last);
* Append elements to an array. If this is not an array, throws
* TypeError.
* Invalidates iterators.
void push_back(dynamic const&);
void push_back(dynamic&&);
* Remove an element from the back of an array. If this is not an array,
* throws TypeError.
* Does not invalidate iterators.
void pop_back();
* Get a hash code. This function is called by a std::hash<>
* specialization, also.
* Throws TypeError if this is an object, array, or null.
std::size_t hash() const;
friend struct TypeError;
struct ObjectImpl;
template <class T> struct TypeInfo;
template <class T> struct CompareOp;
template <class T> struct GetAddrImpl;
template <class T> struct PrintImpl;
explicit dynamic(Array&& array);
template <class T> T const& get() const;
template <class T> T& get();
template <class T> T* get_nothrow() & noexcept;
template <class T> T const* get_nothrow() const& noexcept;
template <class T> T* get_nothrow() && noexcept = delete;
template <class T> T* getAddress() noexcept;
template <class T> T const* getAddress() const noexcept;
template <class T> T asImpl() const;
static char const* typeName(Type);
void destroy() noexcept;
void print(std::ostream&) const;
void print_as_pseudo_json(std::ostream&) const; // see json.cpp
Type type_;
union Data {
explicit Data() : nul(nullptr) {}
~Data() {}
std::nullptr_t nul;
Array array;
bool boolean;
double doubl;
int64_t integer;
std::string string;
* Objects are placement new'd here. We have to use a char buffer
* because we don't know the type here (std::unordered_map<> with
* dynamic would be parameterizing a std:: template with an
* incomplete type right now). (Note that in contrast we know it
* is ok to do this with fbvector because we own it.)
>::type objectBuffer;
} u_;
} // namespace folly
#include <folly/dynamic-inl.h>