Program logic bugs vs input/environmental errors

[Jeremy Powers via Digitalmars-d]

On Mon, Sep 29, 2014 at 8:13 AM, Steven Schveighoffer via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:

> My entire point is, it doesn't matter what is expected or what is treated
> as "correct." what matters is where the input CAME from. To a library
> function, it has no idea. There is no extra type info saying "this
> parameter comes from user input."


>From the method's view, parameters passed in are user input.  Full stop.

One thing that seems to be talked around a bit here is the
separation/encapsulation of things.  It is perfectly fine, and expected,
for a library method to throw exceptions on bad input to the method - even
if this input turns out to be a programming bug elsewhere.  From the
standpoint of the method, it does not know (and does not care) where the
thing ultimately came from - all it knows is that it is input here, and it
is wrong.

If you call a method with bad input, and fail to catch the resulting
exception, then _that_ is a bug, not the method throwing.  It may be
perfectly recoverable to ignore/retry/whatever, or it may be a symptom of
something that should abort the program.  But the method throwing does not
know or care.
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