opImplicitCast/opImplicitCastFrom

[Don]

bearophile wrote:
> In a modern language it's probably good for ALL integral numeric types to be range checked 

I've noticed you've argued for range checking on integral types many 
times. Have you found overflow to be a common bug?
IE, is your comment mainly based on experience, or mainly on theory?

I ask this because I've very rarely encountered that type of bug.
(It could be that it occurs frequently in some problem domains; maybe we 
could work out what they are).