Could you explain that more? “a heavy cost : callbacks are based on std::function (will do a dynamic allocation, and create an indirection)” v.s. “Qt the cost

Could you explain that more? “a heavy cost : callbacks are based on std::function (will do a dynamic allocation, and create an indirection)” v.s. “Qt the cost of doing a `connect` is far smaller” ?? How Qt achieves that using string comparisons at run time? https://doc.qt.io/qt-5/signalsandslots-syntaxes.html https://doc.qt.io/qt-5/signalsandslots-syntaxes.html