conversion from integer or unscoped enumeration type to integer type that cannot represent all values of the original, except where source is a constant expression whose value can be stored exactly in the target type. conversion from an integer type to a floating-point type, except where the source is a constant expression whose value can be stored exactly in the target type. conversion from a long double to double or to float and conversion from double to float, except where the source is a constant expression and overflow does not occur. conversion from a floating-point type to an integer type. List-initialization limits the allowed implicit conversions by prohibiting the following: Otherwise, if the braced-init-list has no elements, T is value-initialized. The type of the temporary is the type referenced by T, unless T is “reference to array of unknown bound of U”, in which case the type of the temporary is the type of x in the declaration U x H, where H is the initializer list (since C++20). The prvalue is then used to direct-initialize the reference (this fails if the reference is a non-const lvalue reference). The prvalue initializes its result object by copy-list-initialization. a prvalue temporary of the type referenced by T is copy-list-initialized, and the reference is bound to that temporary (this fails if the reference is a non-const lvalue reference). Otherwise, if T is a reference type that is not compatible with the type of the element:. Otherwise (if T is not a class type), if the braced-init-list has only one element and either T is not a reference type or is a reference type whose referenced type is same as or is a base class of the type of the element, T is direct-initialized (in direct-list-initialization) or copy-initialized (in copy-list-initialization), except that narrowing conversions are not allowed. Then the enumeration is initialized with the result of converting v to U. 
the conversion from v to U is non-narrowing,.the braced-init-list has only one initializer v that is implicitly convertible to U, and.
the initialization is direct-list-initialization, and.T is an enumeration type that with fixed underlying type U (which is int if the enumeration is scoped and its underlying type is not manually specified), and.If this stage produces an explicit constructor as the best match for a copy-list-initialization, compilation fails (note, in simple copy-initialization, explicit constructors are not considered at all). If the previous stage does not produce a match, all constructors of T participate in overload resolution against the set of arguments that consists of the elements of the braced-init-list, with the restriction that only non-narrowing conversions are allowed.All constructors that take std::initializer_list as the only argument, or as the first argument if the remaining arguments have default values, are examined, and matched by overload resolution against a single argument of type std::initializer_list.Otherwise, the constructors of T are considered, in two phases:.
Otherwise, if T is a specialization of std::initializer_list, the T object is direct-initialized or copy-initialized, depending on context, from a prvalue of the same type initialized from (until C++17) the braced-init-list.Otherwise, if the braced-init-list is empty and T is a class type with a default constructor, value-initialization is performed.Otherwise, if T is an aggregate type, aggregate initialization is performed.
Otherwise, if T is a character array and the braced-init-list has a single element that is an appropriately-typed string literal, the array is initialized from the string literal as usual. If T is an aggregate class and the braced-init-list has a single element of the same or derived type (possibly cv-qualified), the object is initialized from that element (by copy-initialization for copy-list-initialization, or by direct-initialization for direct-list-initialization). The effects of list-initialization of an object of type T are: 12) in a non-static data member initializer that uses the equals sign Explanation
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