I cant figure out why it would be a good idea. Please elaborate.

Mere laziness and DRY (don't repeat yourself). If I have a _sprintf that implements "give a string representation of" I find it sort of superfluous having to repeat the same code in a cast method too. But, as noted, for the (assumed existing) cases where objects not meant to be castable would silently be casted via _sprintf, it might be a horrible idea, losing the error-out-and-die feature.

Thought of that way, a non-existant _sprintf embracing and extending an existant cast method, is probably a lot better, safety-wise, than the other way around, as I thought it of first. In practice, though, I suspect that a lack of _sprintf but not cast, almost never happens.

I think I convinced myself the same. (Still wanted to probe whether it made any sense to others though.)

It did spur the more interesting side of the thread about value casts, though, which I had not anticipated.