Hijacking

[Walter Bright]

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.