Why is "this" enclosed with square brackets here?

Question

#include <Wt/WApplication.h>
#include <Wt/WBreak.h>
#include <Wt/WContainerWidget.h>
#include <Wt/WLineEdit.h>
#include <Wt/WPushButton.h>
#include <Wt/WText.h>

class HelloApplication : public Wt::WApplication
{
public:
HelloApplication(const Wt::WEnvironment& env);

private:
Wt::WLineEdit *nameEdit_;
Wt::WText *greeting_;
};

HelloApplication::HelloApplication(const Wt::WEnvironment& env)
: Wt::WApplication(env)
{
setTitle("Hello world");

root()->addWidget(std::make_unique<Wt::WText>("Your name, please? "));
nameEdit_ = root()->addWidget(std::make_unique<Wt::WLineEdit>());
Wt::WPushButton *button = root()->addWidget(std::make_unique<Wt::WPushButton>("Greet me."));
root()->addWidget(std::make_unique<Wt::WBreak>());
greeting_ = root()->addWidget(std::make_unique<Wt::WText>());
auto greet = [this]{
greeting_->setText("Hello there, " + nameEdit_->text());
};
button->clicked().connect(greet);
}

int main(int argc, char **argv)
{
return Wt::WRun(argc, argv, [](const Wt::WEnvironment& env) {
return std::make_unique<HelloApplication>(env);
});
}

Answer 1

I made a query on the Webtoolkit forum's search bar and there was nothing in particular except some discussion about `connect() and lambda`.

https://redmine.webtoolkit.eu/projects/wt/search?utf8=%E2%9C%93&q=%5Bthis%5D

It's much better to ask your question there, too.

https://redmine.webtoolkit.eu/projects/wt/boards/2

_____
https://en.cppreference.com/w/cpp/language/this
https://en.cppreference.com/w/cpp/language/lambda

Answer 2

Oh, it seems to be the C++'s way of doing anonymous function callbacks. Thanks for the links :)