Hijacking

[Regan Heath]

Walter Bright wrote:
> kris wrote:
>> There's a related problem where a public method is added to a 
>> base-class A (as in your example) but where the signature is *exactly* 
>> that of one existing in derived class B. If A actually calls that new 
>> method internally, "bad things"tm will almost certainly happen, since 
>> B never intended to effectively override the newly-added method in A.
>>
>> This is a very hard problem to isolate yet can be easily remedied by 
>> the compiler. The request was first made two or three years back, and 
>> once or twice since then: you make the "override" keyword *required*.
>>
>> When "override" is required, the compiler can easily trap this related 
>> type of hijacking and avoid such nasty surprises.
> 
> That is a good point. The reason I haven't added it is because I'm not 
> sure how annoying it will be to have to always add the 'override' 
> keyword. It might be one of those things like exception specifications 
> where everyone says it's a good idea but guiltily hate in secret <g>.
> 
> Mitigating factors are private and final methods cannot be overridden.

My vote was, and still is, for 'override' to be mandatory.

Regan