Attempting to use lambda function in static function (C++)

Question

why is this code invalid?. I don't know if I am using the lambda sintax correctly, but based on other posts, it looks fine.

struct foo{
    static int faa(int x);
};

int foo::faa(int x){
    bool isCon = []() {
       return true;
    };

    return isCon();
}

a lambda yields an indeterminate type, not a `bool`, use `auto isCon =` — kmdreko, Dec 01 '17 at 00:16
Related: https://stackoverflow.com/questions/7951377/what-is-the-type-of-lambda-when-deduced-with-auto-in-c11 — Barmar, Dec 01 '17 at 00:38

Francisco Gallego Salido · Answer 1 · 2017-12-01T00:44:07.860

Lambdas have indeterminate type, so you can't know which type will one have. Obviously, the lambda you defined won't be of type bool (it may return a bool, but it's not one), so you would do this instead:

struct foo{
    static int faa(int x);
};

int foo::faa(int x){
    auto isCon = []()->bool {
       return true;
    };

    return isCon();
}

Here, the auto keyword tells the compiler to deduce the type for you. The ->bool expression tells the compiler that the lambda will return a bool.

However, your foo::faa() function returns an int, so a cast may ocurr because your lambda may return a bool (which has nothing to do with the question, but watch out).

Attempting to use lambda function in static function (C++)

1 Answers1