Unique pointer in-class initialization

Question

Suppose I have a unique_ptr member object that I want to initialize in-class, see the code below. Why do I have to use uniform initialization (curly braces)? Th

Answer 1

Because those are the rules. In-class initialisers must use "braces" or "equals"; in fact, the syntactical element is called a brace-or-equal-initializer.

int equals = 42;                      // OK
std::unique_ptr braces{new Foo}; // Also OK

I don't know why parentheses aren't allowed; perhaps to avoid the possibility of the initialisation looking like a function declaration. It can be annoying when there's a difference between direct and brace initialisation:

std::vector bad(6);                     // ERROR: parentheses not allowed
std::vector good{6};                    // OK but not the same
std::vector ugly = std::vector(6); // OK but ugly