mds/Mutation.h: simplify constructors

[stiopaa1]

Signed-off-by: Michal Jarzabek stiopa@gmail.com

[gregsfortytwo]

Hmm. I guess I know you can do this in some cases and I'm guessing recent C++ revisions have added more. But I don't know the rules; is there a benefit beyond Don't Repeat Yourself? Is there a cost?

[stiopaa1]

@gregsfortytwo
Advantages would be as you mentioned no code duplication and then in case you ever wanted to add additional constructors in the future, there is no way to leave those member uninitialised even if you forget to initialise them.
There is no additional cost: (http://en.cppreference.com/w/cpp/language/initializer_list)

If a non-static data member has an default member initializer and also appears in a member initializer list, then member initializer list is executed and the default member initializer is ignored:

struct S {
    int n = 42;   // default member initializer
    S() : n(7) {} // will set n to 7, not 42
};

(since C++11)

The only surprising effect it has in C++11 is that it makes a class a not an aggregate. More information about it here:
http://stackoverflow.com/questions/27118535/c11-aggregate-initialization-for-classes-with-non-static-member-initializers

[gregsfortytwo]

LGTM