Andrei Alexandrescu:
I do agree that it's wrong to _conflate_ the enumerated value
with it ordinal, so in this program neither comparison should
compile without an explicit cast:
enum E1 { A, B }
enum E2 { C, D }
void main() {
E1 a;
assert(a == 0);
assert(a == E2.C);
}
The first one is probably difficult to disallow at this time,
I filed this first problem in 2010-03 (I have not filed the
Enum1==Enum2 problem yet):
http://d.puremagic.com/issues/show_bug.cgi?id=3999
This is a small breaking change, but it doesn't introduce bugs in
already written code, it turns into compile-time errors code that
currently compiles. I think the usual way to solve this
compile-time error is to use a cast (or sometimes use this safe
to!() enhancement:
http://d.puremagic.com/issues/show_bug.cgi?id=8143 ).
C++11 has "solved" this compatibility problem creating another
kind of enum, referred as "enum class":
enum class Foo { V1 = 10 };
int main() {
int b = Foo::V1 == 10;
}
test.cpp: In function 'int main()':
test.cpp:3: error: no match for 'operator==' in '(Foo)10 == 10'
test.cpp:3: note: candidates are: operator==(int, int) <built-in>
The disadvantage of doing this is the complexity increase of the
language.
I don't know how do you estimate how much difficult is to perform
small breaking changes in the language.
Bye,
bearophile
