I use QtConcurrent::blockingMapped() to execute the function on the list of single arguments on multiple threads. It's really great!
But I'd like to do same thing calling the function that takes more than one argument, i.e:
// prototype:
static void openAndProcess(QString FileName, QImage &image);
And this is my data:
QList<QString> fileList;
QList<QImage> qImageList;
And I would like to execute QtConcurrent::blockingMapped() on my openAndProcess() function using both above QLists...
How should I do it?
Thanks in advance!
Create a POD struct with pointers to the data. This is the only way to do this without reimplementing lots of unfun things in QtConcurrent.
Or, consider using QList<QPair<QString, QImage> >, which is effectively the same thing.
Related
In general, the macros QVERIFY, QCOMPARE, etc. shall not be used outside a test function. The reason is, that in case of a failure, they interrupt the test with a return.
If I want to do tests in a function, I should do them by hand and return false if one of them fails. Then call the function with QVERIFY. But when I do this, I miss out the detailed output of the macros like the line where the error occurred.
So I'm looking for a way to use the macros outside of a test function. One solution is to create my own macro that interrupts the test when a macro call in the underlying function fails. The main problem here is to detect when a test has failed. Looking into Qt's code, in case of a fail the variable QTest::failed is set to true. But I don't have access to this variable.
Is there a way to find out if a QtTest macro has failed?
Yeah, Qt does not really offer anything here because the test will not really get interrupted within your own function. The control flow cannot be as easily disturbed. You would need to throw an exception and make sure it's correctly caught.
What I'm doing now is just returning a const char* (works when using a string literal). If the function actually returns something, std::variant can be used, e.g.:
std::variant<MyObject, const char*> createObject() {
// do some preparations
if(preparationsFail) {
return "Error occurred";
// all worked
// ...: create some myObject
return myObject;
}
void MyTest::testFunction() {
auto result = createObject();
if(const char** error = std::get_if<const char*>(&result)) {
QVERIFY2(false, *error); // we get pointer to value, so type is **
}
// else, work with myObject by std::get<MyObject>(result);
}
Not as concise as would be desired, but it works.
It can be made more beautiful by wrapping const char* and, depending on your style, by using std::visit etc. but that's up to you and your style.
I'm trying to use function pointers in DLang (Pointer to function), but it wont compile. All the code on the web on making function pointers, doesn't work for me. This is my code:
tqvar function(tqlist)[string] procs;
procs["divide"] = รท/// cannot implicitly convert expression (&this.divide) of type tqvar delegate(tqlist args) to tqvar function(tqlist) (QScript)
tqvar divide(tqlist args){
tqvar result;
result.ii = true;
result.d = args.read(0).d/args.read(1).d;
return result;
};
I'm using dmd2, on ubuntu.
divide is apparently a delegate, not a function. You can either use a list of delegates instead (just replace function with delegate) or ensure your function is not a delegate.
For the latter: it looks like divide is a class method, not a plain function. Either make it static or move it outside of the class body.
I'm trying to send a QStandardItemModel-derived object to PythonQt, but I'm a little confused on how it needs to be sent. When I was using boost::python I had several controls like boost::noncopyable to ensure I wasn't recreating this object, but sharing it with python. I also had constructs to provide a boost shared pointer to python from inside python.
class Scene : public boost::enable_shared_from_this<Scene>, public QStandardItemModel
In PythonQt, however, I'm not sure what's available. The function call takes a QVariantList for all the function parameters.
QVariant PythonQt::call(PyObject* object, const QString &callable, const QVariantList &args = QVariantList))
What I'm confused about now is how to get my object to python via a QVariant. Since its derived from QStandardItemModel, I figured it would already be register
void MyObject::someFunction(QString fileName)
{
QVariant myObjectV = qVariantFromValue(this);
// send to python
...
}
But this gives me the following error:
'qt_metatype_id' : is not a member of 'QMetaTypeId<MyObject>'
I've tried registering it after I declare my class, but this throws a different error.
class MyObject : public QStandardItemModel
{
Q_OBJECT
...
};
Q_DECLARE_METATYPE(MyObject)
QStandardItemModel::QStandardItemModel(const QStandardItemModel&) is private within this context.
I actually get the error twice--once in header where I add the Q_DECLARE_METATYPE and in another header, which has a class which always derives from QStandardItemModel but is otherwise unrelated.
Is Q_DECLARE_METATYPE even the correct way to go about converting this object to a QVariant?
BOOST_PYTHON_MODULE(scene)
{
class_("Scene");
}
Yes, by default, QVariant can take one of te following types - http://doc.qt.io/qt-4.8/qvariant.html#Type-enum - and they are not enough for your task. You should declare additional types by yourself via qmetatype system. Thus you shoud call qRegisterMetaType() function.
How do you use std.typecons.RefCounted!(T) to make a reference-counted object in D?
I've tried to figure out what std.array.Array does internally by looking at the source, but while I can read the source, I just can't figure what a "payload" is or how it all works when there's things like bitwise struct copying involved, as well as why some things are duplicated in the internal and external structure.
Could anyone provide an example or a link on how to use it to, say, wrap a simple Win32 HANDLE?
Thanks!
Disclaimer: I haven't tested my claims, just read the documentation.
Payload is referring to what is being stored. In your case the payload is the Win32 HANDLE. Since HANDLE is just an integer you wouldn't want to do:
auto refHandle = RefCounted!HANDLE(WhatGetsMeAHandle());
Because a Windows function will need to be called when the handle goes out of scope.
In std.containers.Array what you saw was a struct called Payload, which had a field called _payload. The structure is going to be the storage of the data, accessed through _payload. This provides a level of indirection to be utilized later.
You will notice that RefCounted is actually used on the Array structure. This means the destructor for that struct will only be called when the reference count is 0. So the ~this() inside of Payload is where you would want to clean up the your HANDLE.
What is happening: since struct is a value type, every time the structure goes out of scope the destructor is called, there isn't one for Array, but Payload is wrapped in a RefCounted, the destructor for RefCounted!Payload is also called. And only when the reference count reaches zero is the destructor for Payload itself called.
Now, RefCounted itself has reference semantics, this means that having an Array a, you can then assign to auto b = a; and everything will be copied over, but RefCounted has a postblits defined meaning the data will not be copied, but the reference count will be
incremented.
I will now try and provide you with a wrapper outline for what you want. It will probably help you visualize the information above, but it may not be entirely correct. Let me know if something needs fixing.
struct MyWinWrapper {
struct Payload {
HANDLE _payload;
this(HANDLE h) { _payload = h; }
~this() { freeHandleHere(_payload); }
// Should never perform these operations
this(this) { assert(false); }
void opAssign(MyWinWrapper.Payload rhs) { assert(false); }
}
private alias RefCounted!(Payload, RefCountedAutoInitialize.no) Data;
private Data _data;
this(HANDLE h) { _data = Data(h); }
}
Since there is no default constructor for a struct you will probably want to provide a free function that returns this structure.
Let's Say I Have This Class:
package{
import flash.display.Sprite;
public class Main extends Sprite{
public function Main(){
trace(getAverage(1,2,3));
trace(getAverage(1,2,3,4));
trace(getAverage(1,2,3,4,5));
}
public function getAverage (...numbers) {
var total = 0;
for (var i = 0; i < numbers.length; i++) {
total += numbers [i];
}
return total / numbers.length;
}
}
}
How do I accomplish the "opposite" of this? Namely, how could I now CALL 'getAverage' with a dynamic number of paraemters?
For instance, if I wanted to do something LIKE:
var r:int=Math.random()*6;
var a:Array=new Array();
for (i:int=0;i<r;i++) {
a[i]=Math.random()*22;
}
// Now I have 'r' Number Of Parameters Stored In 'a'
// How Do I Call getAverage, with all the values in 'a'??
// getAverage(a) isn't right, is it?
// I'm looking for something similar to getAverage(a[0],a[1],a[...]);
var av:Number=getAverage(???);
What I want to know, is if I have a function that takes a variable number of arguments, that's great, but how can I CALL IT with a variable number of arguments, when that number isn't known at runtime? Possibly it's impossible... I'm just not sure, since 'callLater' seems to be able to take an array and generate a dynamic number of parameters from it somehow...
NOTE: Answers consisting solely of "Why Do You Want To Do This?", will be downvoted.
P.S. This IS NOT about calculating Averages! I REALIZE There Are Way Simpler Ways Of Doing All Of This! (I could just write getAverage to accept a single array as its only parameter) The Above is just an EXAMPLE to Illustrate my Question. HOW TO PASS A DYNAMIC NUMBER OF PARAMETERS TO A FUNCTION?
Is this what you're looking for?
var av:Number = getAverage.apply(null, a);
Dave is correct. You can use the apply method of a function to pass in an Array of arguments.
Here is a better explanation of how it works and what the arguments of apply are:
http://www.adobe.com/livedocs/flash/9.0/ActionScriptLangRefV3/Function.html
Also note that you can use the call method to do the same thing but using ...args (comma-delimited list) instead, but apply would be more suitable to your situation.
The problem with your question is that the arguments object is already an Array and using (...args) already provides you with a dynamic way to pass any number of arguments you require. Sorry about the previous answer, wasn't thinking straight...
You can create an array or an object with those parameters and pass that object to that function. That's just normal.
Flash has a rather strong introspection capabilities. So, instead of passing a number of objects, you just pass a single dynamic object with any number of attributes you need:
var ob:Object={arg1:"value1", arg2:8};
var arg:String="arg4";
ob["arg3"]=8;
ob[arg]=18;
trace (ob.hasOwnProperty("arg1"));
trace (ob.arg3);
trace (ob.arg4);
That should cover just about any use case you might need. The downside is that this allows for some rather clever and hard to trace bugs. :-)