Wednesday, February 8, 2012

const T =shadow-type of T;const T&=distinct type from T&

(background: the nitty gritty of overload/overriding rules are too complicated...)

I feel overloading and overriding has consistent rules. Take 2 same-name functions (single-param functions for simplicity) and ignore their host classes. If the 2 can overload each other, then their parameters are considered distinct. That means they can't override each other (if they were inserted into a inheritance tree).

Conversely, if the 2 can override each other, then their parameter types are considered "identical" so they can't overload each other (if set "free").

Q: We know function overloading forbids 2 overloads with identical parameter sets. How about const, i.e. If 2 functions' parameters differ only in const, can they have identical names?
A: No. ARM P308 explains that compiler's (static) "resolution" (based on argument type) will fail to pick a winner among the 2. It's ambiguous.
A: therefore, in the overloading context, const SomeType is a "shadow type" and does NOT count as a distinct type.

However, if 2 functions' parameters have this difference -- const T& vs T&, then distinct types, so the 2 functions can have identical names. Exaplained in ARM.

Similarly, 2 overloads can overload based on const T* vs T* -- distinct types.


Q: We know method overriding requires exact parameter match. How about const? Can an override add or remove const?
A: whatever the answer, this is sloppy. No justification.
A: yes according to my test. Adding the const makes no difference -- runtime binding unobstructed.
A: therefore, in the overriding context, const SomeType is a "shadow type" and does NOT count as a distinct type.

However, my test shows const T& vs T& do make a difference -- runtime binding disabled. These are considered 2 distinct types.

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