c++11 For structs is there an automatic way to initialise a new variable that does not involved writing a constructor?

I think that I vaguely recall that one of the newer c++ standards (maybe its c++11, or maybe 14?...17??) allows you to initialise a struct, whereby you can define a struct and then initialise it without having to write a constructor.

E.g.:

struct test
{
    int a;
    int b;
    std::string str;
}

int main()
{
    std::map<int, test> test_map;
    test_map[0] = test(1, 2, "test1"); // This is the line in question
    // Or it might be more like: test_map[0] = test{1, 2, "test1"};
    return 0;
}

I can't recall the name of this special initialisation (or if it even exists)!. So my questions are:

• Is there some new mechanism to achieve this without writing a constructor in the struct "test"?
• If so, what is it called (so I can read more about it).

If this "feature" does not exist then please put me out of my misery!, it could be that my imagination has made this up...