I am trying to use QtConcurrent::mapped
into a QVector<QString>
. I already tried a lot of methods, but it seems there are always problems with overloading.
QVector<QString> words = {"one", "two", "three", "four"};
using StrDouble = std::pair<QString, double>;
QFuture<StrDouble> result = QtConcurrent::mapped<StrDouble>(words, [](const QString& word) -> StrDouble {
return std::make_pair(word + word, 10);
});
This snippet returns the following error:
/home/lhahn/dev/cpp/TestLambdaConcurrent/mainwindow.cpp:23: error: no matching function for call to ‘mapped(QVector<QString>&, MainWindow::MainWindow(QWidget*)::<lambda(const QString&)>)’
});
^
I saw this post, which says that Qt cannot find the return value of the lambda, so you have to use std::bind
with it. If I try this:
using StrDouble = std::pair<QString, double>;
using std::placeholders::_1;
auto map_fn = [](const QString& word) -> StrDouble {
return std::make_pair(word + word, 10.0);
};
auto wrapper_map_fn = std::bind(map_fn, _1);
QFuture<StrDouble> result = QtConcurrent::mapped<StrDouble>(words, wrapper_map_fn);
But the the error is still similar:
/home/lhahn/dev/cpp/TestLambdaConcurrent/mainwindow.cpp:28: error: no matching function for call to ‘mapped(QVector<QString>&, std::_Bind<MainWindow::MainWindow(QWidget*)::<lambda(const QString&)>(std::_Placeholder<1>)>&)’
QFuture<StrDouble> result = QtConcurrent::mapped<StrDouble>(words, wrapper_map_fn);
^
I also tried wrapping the lambda inside std::function
but unfortunately similar results.
- Note that this example is just for reproduction, I need a lambda because I am also capturing variables in my code.