Variables passed by the C + + lambda expression Room are not mutable by default

I have encountered the following questions:

int count=0;    Listener->ontouchmoved=[count] (touch* t,event* e) {        count++;        Log ("ontouchmoved");            };

The compilation errors under Xcode are:cannot assign to a variable captured by copy in a non-mutable lambda.

So how to solve it?

In a lambda expression, the captured variable is immutable by default.

This function, call operator, or operator template is declared const (9.3.1) if and only if the lambda-expression ' s paramete R-declaration-clause is isn't followed by mutable.

So if you want to change the value of the variable within the AMBDA expression, rewrite the following:

int count=0;    Listener->ontouchmoved=[count] (touch* t,event* e) mutable{        count++;        Log ("ontouchmoved");            };

Variables passed by the C + + lambda expression Room are not mutable by default