I'm trying to get the result of a script simple operation on the C++ side.
I create a QScriptValue (myvar) and call engine.globalObject().setProperty("result", myvar);
Then I evaluate "result = anothervar + 7;" The evaluate method return value is OK but the variable result is not OK.
If the script is "result = anothervar + 7; a=1" then the result value is OK.
It looks too stupid to be a Qt bug so what did I miss ?
Thanks
Jeff
From your answer to my comment, I'm assuming you're keeping the QScriptValue myvar instance around, and look at it after calling evaluate():
QScriptEngine e;
QScriptValue myvar( 1.0 );
e.globalObject().setProperty( "result", myvar );
e.globalObject().setProperty( "anotherVar", QScriptValue( 14 ) );
const QScriptValue s = e.evaluate( "result = anotherVar + 7;" );
qDebug() << s.toVariant();
qDebug() << e.globalObject().property("result").toVariant();
qDebug() << myvar.toVariant();
This will print 2x "QVariant(double,21)" and once "QVariant(double,1)". That is expected behaviour, here's why:
In JavaScript, everything is an object, and you are only dealing with references to objects, not the objects themselves (if you know Java, this is similar to int vs. Integer). So, what the assignment result = anotherVar + 7; does is replace the object represented by myvar as the global object's "result" property with the object that results from the expression anotherVar + 7. Meanwhile, the QScriptValue myvar still references the (old) object, which otherwise would be up for grabs by the garbage-collecter at this point.
About the addition of a=1 to fix the problem: I can't reproduce that here. The first debug statement prints the value of a, of course, but the second and third are unchanged.
The solution to your problem, therefore, is to always re-get the "result" property from the engine whenever you need it (using engine.globalObject().property("result")), or—in other words—QScriptValue doesn't track assigments.
If you do want to track assignment, you need to turn it into a method call: Implement result as a custom class with an assign() method, and replace assignment (=) with result.assign( anotherVal + 7 );.