I'm glad we're discussing this. There's an important misunderstanding.
On 11/18/2013 2:16 PM, Jonathan M Davis wrote:
But that would just duplicate the validation. You validate by parsing the
string, and you extract the necessary data from it by parsing it. Validating
the data first would just double the work - on top of the fact that strings are
most likely to have come from outside the program rather than having been
generated internally and then parsed internally. This is exactly the sort of
case where I think that separate validation makes no sense. Separate
validation only makes sense when the result is _less_ overhead, not more.
The point of asserts is that they are supposed to be redundant. (If they were
not redundant, then they would trip and you'd have a program bug.) Asserts are
there to detect program bugs, not to validate input data. This is also why the
optimizer can remove asserts without affecting the meaning of the code.
Separate validation is of benefit when the caller can avoid the validation in
most cases, and the function itself doesn't need to do it, so the validition
only occurs when the caller needs it. If the validation has to be done anyway,
then there's no point in having separate validation. It just increases
overhead.
Consider again that std.datetime is chock full of code that requires the
underlying functions to not throw.
Anytime there is code of the pattern:
try {
func();
} catch (Exception e) {
assert(0, "func() should not have thrown");
}
then func() has the wrong API or is being misused.
Again, data validation and bug checking are two very different things and should
not be combined.
Note that I have screwed this up myself in the std.uni API.
