Class model

external/catch.hpp:6706–6723

                };
                template <typename Fun>
                struct model : public callable {
                    model(Fun&& fun) : fun(std::move(fun)) {}
                    model(Fun const& fun) : fun(fun) {}

                    model<Fun>* clone() const override { return new model<Fun>(*this); }

                    void call(Chronometer meter) const override {
                        call(meter, is_callable<Fun(Chronometer)>());
                    }
                    void call(Chronometer meter, std::true_type) const {
                        fun(meter);
                    }
                    void call(Chronometer meter, std::false_type) const {
                        meter.measure(fun);
                    }

                    Fun fun;
                };

                struct do_nothing { void operator()() const {} };