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# std.json

Implements functionality to read and write JavaScript Object Notation values.
JavaScript Object Notation is a lightweight data interchange format commonly used in web services and configuration files. It's easy for humans to read and write, and it's easy for machines to parse and generate.
Warning: While JSONValue is fine for small-scale use, at the range of hundreds of megabytes it is known to cause and exacerbate GC problems. If you encounter problems, try replacing it with a stream parser. See also https://forum.dlang.org/post/dzfyaxypmkdrpakmycjv@forum.dlang.org.
License:
Boost License 1.0.
Authors:
Jeremie Pelletier, David Herberth

References http://json.org/, http://seriot.ch/parsing_json.html

Source std/json.d

Examples:

    import std.conv : to;

    // parse a file or string of json into a usable structure
    string s = `{ "language": "D", "rating": 3.5, "code": "42" }`;
    JSONValue j = parseJSON(s);
    // j and j["language"] return JSONValue,
    // j["language"].str returns a string
    writeln(j["language"].str); // "D"
    writeln(j["rating"].floating); // 3.5

    // check a type
    long x;
    if (const(JSONValue)* code = "code" in j)
    {
        if (code.type() == JSONType.integer)
            x = code.integer;
        else
            x = to!int(code.str);
    }

    // create a json struct
    JSONValue jj = [ "language": "D" ];
    // rating doesnt exist yet, so use .object to assign
    jj.object["rating"] = JSONValue(3.5);
    // create an array to assign to list
    jj.object["list"] = JSONValue( ["a", "b", "c"] );
    // list already exists, so .object optional
    jj["list"].array ~= JSONValue("D");

    string jjStr = `{"language":"D","list":["a","b","c","D"],"rating":3.5}`;
    writeln(jj.toString); // jjStr

enum `JSONFloatLiteral`: string;
  String literals used to represent special float values within JSON strings.
  `nan`
    string representation of floating-point NaN
  `inf`
    string representation of floating-point Infinity
  `negativeInf`
    string representation of floating-point negative Infinity
enum `JSONOptions`: int;
  Flags that control how json is encoded and parsed.
  `none`
    standard parsing
  `specialFloatLiterals`
    encode NaN and Inf float values as strings
  `escapeNonAsciiChars`
    encode non ascii characters with an unicode escape sequence
  `doNotEscapeSlashes`
    do not escape slashes ('/')
  `strictParsing`
    Strictly follow RFC-8259 grammar when parsing
enum `JSONType`: byte;
  JSON type enumeration
  `null_`
  `string`
  `integer`
  `uinteger`
  `float_`
  `array`
  `object`
  `true_`
  `false_`
    Indicates the type of a JSONValue.
struct `JSONValue`;
  JSON value node
  const pure nothrow @nogc @property @safe JSONType `type`();
    Returns the JSONType of the value stored in this structure.
    Examples:

        string s = "{ \"language\": \"D\" }";
        JSONValue j = parseJSON(s);
        writeln(j.type); // JSONType.object
        writeln(j["language"].type); // JSONType.string

  const pure @property scope @trusted string `str`() return;
  pure nothrow @nogc @property @trusted string `str`(return scope string `v`) return;
    Value getter/setter for JSONType.string.
    Throws:
    JSONException for read access if type is not JSONType.string.
    Examples:

        JSONValue j = [ "language": "D" ];

        // get value
        writeln(j["language"].str); // "D"

        // change existing key to new string
        j["language"].str = "Perl";
        writeln(j["language"].str); // "Perl"

  const pure @property @safe long `integer`();
  pure nothrow @nogc @property @safe long `integer`(long `v`);
    Value getter/setter for JSONType.`integer`.
    Throws:
    JSONException for read access if type is not JSONType.`integer`.
  const pure @property @safe ulong `uinteger`();
  pure nothrow @nogc @property @safe ulong `uinteger`(ulong `v`);
    Value getter/setter for JSONType.`uinteger`.
    Throws:
    JSONException for read access if type is not JSONType.`uinteger`.
  const pure @property @safe double `floating`();
  pure nothrow @nogc @property @safe double `floating`(double `v`);
    Value getter/setter for JSONType.float_. Note that despite the name, this is a 64-bit double, not a 32-bit float.
    Throws:
    JSONException for read access if type is not JSONType.float_.
  const pure @property @safe bool `boolean`();
  pure nothrow @nogc @property @safe bool `boolean`(bool `v`);
    Value getter/setter for boolean stored in JSON.
    Throws:
    JSONException for read access if this.type is not JSONType.true_ or JSONType.false_.
    Examples:

        JSONValue j = true;
        writeln(j.boolean); // true

        j.boolean = false;
        writeln(j.boolean); // false

        j.integer = 12;
        import std.exception : assertThrown;
        assertThrown!JSONException(j.boolean);

  inout pure @property ref @system inout(JSONValue[string]) `object`() return;
  pure nothrow @nogc @property @trusted JSONValue[string] `object`(return scope JSONValue[string] `v`);
    Value getter/setter for JSONType.`object`.
    Throws:
    JSONException for read access if type is not JSONType.`object`.

    Note this is @system because of the following pattern:

        auto a = &(json.object());
        json.uinteger = 0;        // overwrite AA pointer
        (*a)["hello"] = "world";  // segmentation fault

  inout pure @property @trusted inout(JSONValue[string]) `objectNoRef`();
    Value getter for JSONType.object. Unlike object, this retrieves the object by value and can be used in @safe code.
    A caveat is that, if the returned value is null, modifications will not be visible:

        JSONValue json;
        json.object = null;
        json.objectNoRef["hello"] = JSONValue("world");
        assert("hello" !in json.object);

    Throws:
    JSONException for read access if type is not JSONType.object.
  inout pure @property ref scope @system inout(JSONValue[]) `array`() return;
  pure nothrow @nogc @property scope @trusted JSONValue[] `array`(return scope JSONValue[] `v`);
    Value getter/setter for JSONType.`array`.
    Throws:
    JSONException for read access if type is not JSONType.`array`.

    Note this is @system because of the following pattern:

        auto a = &(json.array());
        json.uinteger = 0;  // overwrite array pointer
        (*a)[0] = "world";  // segmentation fault

  inout pure @property @trusted inout(JSONValue[]) `arrayNoRef`();
    Value getter for JSONType.array. Unlike array, this retrieves the array by value and can be used in @safe code.
    A caveat is that, if you append to the returned array, the new values aren't visible in the

    JSONValue

        JSONValue json;
        json.array = [JSONValue("hello")];
        json.arrayNoRef ~= JSONValue("world");
        assert(json.array.length == 1);

    Throws:
    JSONException for read access if type is not JSONType.array.
  const pure nothrow @nogc @property @safe bool `isNull`();
    Test whether the type is JSONType.null_
  inout const pure @property @safe inout(T) `get`(T)();
  inout pure @property @trusted inout(T) `get`(T : JSONValue[string])();
    Generic type value getter A convenience getter that returns this JSONValue as the specified D type.

    Note only numeric, bool, string, JSONValue[string] and JSONValue[] types are accepted

    Throws:
    JSONException if T cannot hold the contents of this JSONValue ConvException in case of integer overflow when converting to T
    Examples:

        import std.exception;
        import std.conv;
        string s =
        `{
            "a": 123,
            "b": 3.1415,
            "c": "text",
            "d": true,
            "e": [1, 2, 3],
            "f": { "a": 1 },
            "g": -45,
            "h": ` ~ ulong.max.to!string ~ `,
         }`;

        struct a { }

        immutable json = parseJSON(s);
        writeln(json["a"].get!double); // 123.0
        writeln(json["a"].get!int); // 123
        writeln(json["a"].get!uint); // 123
        writeln(json["b"].get!double); // 3.1415
        assertThrown!JSONException(json["b"].get!int);
        writeln(json["c"].get!string); // "text"
        writeln(json["d"].get!bool); // true
        assertNotThrown(json["e"].get!(JSONValue[]));
        assertNotThrown(json["f"].get!(JSONValue[string]));
        static assert(!__traits(compiles, json["a"].get!a));
        assertThrown!JSONException(json["e"].get!float);
        assertThrown!JSONException(json["d"].get!(JSONValue[string]));
        assertThrown!JSONException(json["f"].get!(JSONValue[]));
        writeln(json["g"].get!int); // -45
        assertThrown!ConvException(json["g"].get!uint);
        writeln(json["h"].get!ulong); // ulong.max
        assertThrown!ConvException(json["h"].get!uint);
        assertNotThrown(json["h"].get!float);

  this(T)(T `arg`)
  if (!isStaticArray!T);
  this(T)(ref T `arg`)
  if (isStaticArray!T);
  inout this(T : JSONValue)(inout T `arg`);
    Constructor for JSONValue. If `arg` is a JSONValue its value and type will be copied to the new JSONValue. Note that this is a shallow copy: if type is JSONType.object or JSONType.array then only the reference to the data will be copied. Otherwise, `arg` must be implicitly convertible to one of the following types: typeof(null), string, ulong, long, double, an associative array V[K] for any V and K i.e. a JSON object, any array or bool. The type will be set accordingly.
    Examples:

        JSONValue j = JSONValue( "a string" );
        j = JSONValue(42);

        j = JSONValue( [1, 2, 3] );
        writeln(j.type); // JSONType.array

        j = JSONValue( ["language": "D"] );
        writeln(j.type); // JSONType.object

  enum JSONValue `emptyObject`;
    An enum value that can be used to obtain a JSONValue representing an empty JSON object.
    Examples:

        JSONValue obj1 = JSONValue.emptyObject;
        writeln(obj1.type); // JSONType.object
        obj1.object["a"] = JSONValue(1);
        writeln(obj1.object["a"]); // JSONValue(1)

        JSONValue obj2 = JSONValue.emptyObject;
        assert("a" !in obj2.object);
        obj2.object["b"] = JSONValue(5);
        assert(obj1 != obj2);

  enum JSONValue `emptyArray`;
    An enum value that can be used to obtain a JSONValue representing an empty JSON array.
    Examples:

        JSONValue arr1 = JSONValue.emptyArray;
        writeln(arr1.type); // JSONType.array
        writeln(arr1.array.length); // 0
        arr1.array ~= JSONValue("Hello");
        writeln(arr1.array.length); // 1
        writeln(arr1.array[0]); // JSONValue("Hello")

        JSONValue arr2 = JSONValue.emptyArray;
        writeln(arr2.array.length); // 0
        assert(arr1 != arr2);

  inout pure ref @safe inout(JSONValue) `opIndex`(size_t `i`);
    Array syntax for json arrays.
    Throws:
    JSONException if type is not JSONType.array.
    Examples:

        JSONValue j = JSONValue( [42, 43, 44] );
        writeln(j[0].integer); // 42
        writeln(j[1].integer); // 43

  inout pure ref @safe inout(JSONValue) `opIndex`(return scope string `k`);
    Hash syntax for json objects.
    Throws:
    JSONException if type is not JSONType.object.
    Examples:

        JSONValue j = JSONValue( ["language": "D"] );
        writeln(j["language"].str); // "D"

  void `opIndexAssign`(T)(auto ref T `value`, string `key`);
  void `opIndexAssign`(T)(T `arg`, size_t `i`);
    Operator sets `value` for element of JSON object by `key`.
    If JSON value is null, then operator initializes it with object and then sets `value` for it.
    Throws:
    JSONException if type is not JSONType.object or JSONType.null_.
    Examples:

        JSONValue j = JSONValue( ["language": "D"] );
        j["language"].str = "Perl";
        writeln(j["language"].str); // "Perl"

    Examples:

        JSONValue j = JSONValue( ["Perl", "C"] );
        j[1].str = "D";
        writeln(j[1].str); // "D"

  inout @safe inout(JSONValue)* `opBinaryRight`(string op : "in")(string `k`);
    Support for the in operator.
    Tests wether a key can be found in an object.
    Returns:
    when found, the inout(JSONValue)* that matches to the key, otherwise null.
    Throws:
    JSONException if the right hand side argument JSONType is not object.
    Examples:

        JSONValue j = [ "language": "D", "author": "walter" ];
        string a = ("author" in j).str;
        *("author" in j) = "Walter";
        writeln(j["author"].str); // "Walter"

  const pure nothrow @nogc @safe bool `opEquals`(const JSONValue `rhs`);
  const pure nothrow @nogc @trusted bool `opEquals`(const ref JSONValue `rhs`);
    Examples:

        writeln(JSONValue(0u)); // JSONValue(0)
        writeln(JSONValue(0u)); // JSONValue(0.0)
        writeln(JSONValue(0)); // JSONValue(0.0)

  @system int `opApply`(scope int delegate(size_t index, ref JSONValue) `dg`);
    Implements the foreach `opApply` interface for json arrays.
  @system int `opApply`(scope int delegate(string key, ref JSONValue) `dg`);
    Implements the foreach `opApply` interface for json objects.
  const @safe string `toString`(in JSONOptions `options` = JSONOptions.none);
    Implicitly calls toJSON on this JSONValue.
    options can be used to tweak the conversion behavior.
  const void `toString`(Out)(Out `sink`, in JSONOptions `options` = JSONOptions.none);
  const @safe string `toPrettyString`(in JSONOptions `options` = JSONOptions.none);
    Implicitly calls toJSON on this JSONValue, like toString, but also passes true as pretty argument.
    options can be used to tweak the conversion behavior
  const void `toPrettyString`(Out)(Out `sink`, in JSONOptions `options` = JSONOptions.none);
JSONValue `parseJSON`(T)(T `json`, int `maxDepth` = -1, JSONOptions `options` = JSONOptions.none)
if (isSomeFiniteCharInputRange!T);
  Parses a serialized string and returns a tree of JSON values.
  Throws:
  JSONException if string does not follow the JSON grammar or the depth exceeds the max depth, ConvException if a number in the input cannot be represented by a native D type.
  Parameters:

  T `json` | json-formatted string to parse
  int `maxDepth` | maximum depth of nesting allowed, -1 disables depth checking
  JSONOptions `options` | enable decoding string representations of NaN/Inf as float values

JSONValue `parseJSON`(T)(T `json`, JSONOptions `options`)
if (isSomeFiniteCharInputRange!T);
  Parses a serialized string and returns a tree of JSON values.
  Throws:
  JSONException if the depth exceeds the max depth.
  Parameters:

  T `json` | json-formatted string to parse
  JSONOptions `options` | enable decoding string representations of NaN/Inf as float values

@safe string `toJSON`(const ref JSONValue `root`, in bool `pretty` = false, in JSONOptions `options` = JSONOptions.none);
  Takes a tree of JSON values and returns the serialized string.
  Any Object types will be serialized in a key-sorted order.
  If `pretty` is false no whitespaces are generated. If `pretty` is true serialized string is formatted to be human-readable. Set the JSONOptions.specialFloatLiterals flag is set in `options` to encode NaN/Infinity as strings.
void `toJSON`(Out)(auto ref Out `json`, const ref JSONValue `root`, in bool `pretty` = false, in JSONOptions `options` = JSONOptions.none)
if (isOutputRange!(Out, char));
class `JSONException`: object.Exception;
  Exception thrown on JSON errors

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