Re: A case where Ada defaults to unsafe?

[Ted Dennison<dennison@telepath.com>]

In article <3C35675D.276C2D81@canal-plus.fr>, Thierry Lelegard says...
>
>Maybe the actual question should be "why are there two distinct formats,
>with and without short-circuit?"
>
>"and then" has an actual added value over "and" (the short-circuit).
>On the other hand, what is the added value of "and"? What can be
>achieved by "and" that could not be by "and then" (except side-effect,
>which is a dirty practice)?

Again, I wish people would read the rationale before saying stuff like this. It
is exaplained there. 

One issue is that you may indeed want the side effects of both expressions
(dirty practice or no). Another is that the compiler is not free to reorder your
expressions for efficiency with the short-circuit forms, even if it turns out
that you really don't care what order they are performed in (which is usually
going to be the case). Another is that there are some circumstances where a
short-circuit is going to be *slower* than a non-short circuit calculation.
After all, a short-circuit implies an extra branch instruction, whereas normal
"and" is a simple integer-unit operation. Plus, if the typical eventuality is to
make it through to the last expression, then all those extra checks are a big
waste.

Now I know Robert Dewar is on record as saying that most of these issues either
don't apply on modern processors, or were never taken advantage of by any
compiler. But the above was the initial reasoning for not short-circuiting.

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