json: Add operator[] to QJsonValue for implicit object and array access

Saves a lot of manual toArray() and toObject() calls when the
JSON structure is usually known anyways. Read only access for now.

Change-Id: I5fd787144198e0443e4da285a11ce2597b66f99f
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/json/qjsonvalue.cpp

@@ -642,6 +642,58 @@ QJsonObject QJsonValue::toObject() const
     return toObject(QJsonObject());
 }
 
+/*!
+    Returns a QJsonValue representing the value for the key \a key.
+
+    Equivalent to calling toObject().value(key).
+
+    The returned QJsonValue is QJsonValue::Undefined if the key does not exist,
+    or if isObject() is false.
+
+    \since 5.10
+
+    \sa QJsonValue, QJsonValue::isUndefined(), QJsonObject
+ */
+const QJsonValue QJsonValue::operator[](const QString &key) const
+{
+    if (!isObject())
+        return QJsonValue(QJsonValue::Undefined);
+
+    return toObject().value(key);
+}
+
+/*!
+    \overload
+    \since 5.10
+*/
+const QJsonValue QJsonValue::operator[](QLatin1String key) const
+{
+    if (!isObject())
+        return QJsonValue(QJsonValue::Undefined);
+
+    return toObject().value(key);
+}
+
+/*!
+    Returns a QJsonValue representing the value for index \a i.
+
+    Equivalent to calling toArray().at(i).
+
+    The returned QJsonValue is QJsonValue::Undefined, if \a i is out of bounds,
+    or if isArray() is false.
+
+    \since 5.10
+
+    \sa QJsonValue, QJsonValue::isUndefined(), QJsonArray
+ */
+const QJsonValue QJsonValue::operator[](int i) const
+{
+    if (!isArray())
+        return QJsonValue(QJsonValue::Undefined);
+
+    return toArray().at(i);
+}
+
 /*!
     Returns \c true if the value is equal to \a other.
  */

src/corelib/json/qjsonvalue.h

@@ -137,6 +137,10 @@ public:
     QJsonObject toObject() const;
     QJsonObject toObject(const QJsonObject &defaultValue) const;
 
+    const QJsonValue operator[](const QString &key) const;
+    const QJsonValue operator[](QLatin1String key) const;
+    const QJsonValue operator[](int i) const;
+
     bool operator==(const QJsonValue &other) const;
     bool operator!=(const QJsonValue &other) const;
 

tests/auto/corelib/json/tst_qtjson.cpp

@@ -145,6 +145,8 @@ private Q_SLOTS:
     void parseErrorOffset_data();
     void parseErrorOffset();
 
+    void implicitValueType();
+
 private:
     QString testDataDir;
 };
@@ -2908,5 +2910,33 @@ void tst_QtJson::parseErrorOffset()
     QCOMPARE(error.offset, errorOffset);
 }
 
+void tst_QtJson::implicitValueType()
+{
+    QJsonObject rootObject{
+        {"object", QJsonObject{{"value", 42}}},
+        {"array", QJsonArray{665, 666, 667}}
+    };
+
+    QJsonValue objectValue = rootObject["object"];
+    QCOMPARE(objectValue["value"].toInt(), 42);
+    QCOMPARE(objectValue["missingValue"], QJsonValue(QJsonValue::Undefined));
+    QCOMPARE(objectValue[123], QJsonValue(QJsonValue::Undefined));
+    QCOMPARE(objectValue["missingValue"].toInt(123), 123);
+
+    QJsonValue arrayValue = rootObject["array"];
+    QCOMPARE(arrayValue[1].toInt(), 666);
+    QCOMPARE(arrayValue[-1], QJsonValue(QJsonValue::Undefined));
+    QCOMPARE(arrayValue["asObject"], QJsonValue(QJsonValue::Undefined));
+    QCOMPARE(arrayValue[-1].toInt(123), 123);
+
+    const QJsonObject constObject = rootObject;
+    QCOMPARE(constObject["object"]["value"].toInt(), 42);
+    QCOMPARE(constObject["array"][1].toInt(), 666);
+
+    QJsonValue objectAsValue(rootObject);
+    QCOMPARE(objectAsValue["object"]["value"].toInt(), 42);
+    QCOMPARE(objectAsValue["array"][1].toInt(), 666);
+}
+
 QTEST_MAIN(tst_QtJson)
 #include "tst_qtjson.moc"