Qt C++ connect signal with non-void signature to lambda

I want to connect a signal with non-void signature to a lambda function. My code looks like the following

QTimeLine *a = new QTimeLine(DURATION, this); connect(a, &QTimeLine::valueChanged, [a,this](qreal r) mutable { this->setMaximumHeight(r);});

in a way similar to the SIGNAL-SLOT approach:

connect(a, SIGNAL(valueChanged(qreal),this,SLOT(doStuff(qreal)));

My connect-to-lambda compiles, but it won't change this->height(). What did I get wrong? How should I write the lambda so that it takes the qreal from valueChanged? I read the related documentation, but I couldn't find useful examples.

****EDIT****

In fact it works, I was getting the QTimeLine settings wrong. And yes, I don't need to capture a. I was trying to animate a custom insertRow() method of a QTableWidget. I also made the lambda change the height of the table row instead of the contained widget's. For reference, here's the working snippet:

QTimeLine *a = new QTimeLine(DURATION,this);
connect(a,&QTimeLine::valueChanged,[this](qreal r) mutable {
     this->list->setRowHeight(0,r * ROW::HEIGHT);
     });
a->start();

Thanks a lot for the quick replies anyway.

Solution

Should just work. Here is a complete SSCCE that demonstrates it working. Check what you are doing different in principles.

main.cpp

#include <QTimeLine>
#include <QObject>
#include <QDebug>
#include <QCoreApplication>

class Foo
{
    void setMaximumHeight(int h) {height = h; qDebug() << "Height:" << height;}
    public:
    void doStuff() { QObject::connect(&timeLine, &QTimeLine::valueChanged, [this](qreal r) mutable { setMaximumHeight(r);}); timeLine.start(); }
    int maximumHeight() const { return height; }
    int height{0};
    int DURATION{100};
    QTimeLine timeLine{DURATION};
};

int main(int argc, char **argv)
{
    QCoreApplication application(argc, argv);
    Foo foo;
    foo.doStuff();
    return application.exec();
}

main.pro

TEMPLATE = app
TARGET = main
QT = core
CONFIG += c++11
SOURCES += main.cpp

Build and Run

qmake && make && ./main