Why can in-class initializers only use = or {}?
c++, c++11, curly-braces, initializer
Solution
I am not 100% positive about this, but this might be to prevent a syntax ambiguity. For example, consider the following class:
class BadTimes {
struct Overloaded;
int Overloaded; // Legal, but a very strange idea.
int confusing(Overloaded); // <-- This line
};
What does the indicated line mean? As written, this is a declaration of a member function named `confusing` that accepts as a parameter an object of type `Overloaded` (whose name isn't specified in the function declaration) and returns an `int`. If C++11 were to allow initializers to use parentheses, this would be ambiguous, because it could also be a definition of a member of type `int` named `confusing` that is initialized to the value of the data member `Overloaded`. (This is related to the current issue with the Most Vexing Parse.)
By requiring curly braces, this ambiguity is removed:
class BadTimes {
struct Overloaded;
int Overloaded; // Legal, but a very strange idea.
int confusing{Overloaded}; // <-- This line
};
Now, it's clear that `confusing` is actually an `int` initialized to the value of `Overloaded`, because there's no way to read it as a function declaration.
Hope this helps!
Problem
In-class initializers (C++11 feature) must be enclosed in curly braces or follow a = sign. They may not be specified inside parenthesis. What is the reason for this?