input validation

[Andrei Alexandrescu]

bearophile wrote:
> Andrei Alexandrescu:
>> Binary search is rather common.
> 
> Oh, yes, sorry, I meant among the ones you have listed there...

Of five, three are frequent (linear, binary, Boyer-Moore), one is a form
of set intersection (find sorted in sorted), and the odd one is:

find(a, assumeSorted(b));

This is rare but has excellent best-case complexity (is it O(a.length /
b.length)?) and is easy to add for completeness.

>> As an aside, your use of "index" suggests you return integrals out
>> of the function. IMHO that's strongly unrecommended.
> 
> I don't want to use too much of your time (that it may be better
> spent with your new child), but I don't understand what you mean. 
> That index() function is meant the index position of the item or
> sub-sequence into the bigger array (or iterable), and it returns -1
> if not found. This is an usual design.

This is an extremely sloppy design. That it is usual doesn't make things
any better!

> Some people think that such controls for -1 value aren't always done,
> so to avoid that and some bugs, it's better to raise something like
> IndexException when the needle isn't found.

Yah, this is the subject of a long rant but in short: returning int from 
find means that essentially that find is unusable with anything except 
random access structures. This in turn means you'd have to have 
different means, APIs, and user code to deal with e.g. lists, in spite 
of the fact that linear search is the same boring thing for all: look at 
the current thing, yes/no, move on to the next thing. IMHO ever since 
the STL has seen the light of day there is no excuse, not even sheer 
ignorance, to ever traffic in integers as a mean to access elements in 
containers, in any language that has even the most modest parameterized 
types capability.

Returning int from find is an insult. To add injury to it, have find 
also return an int for a list.

"Is this item in this list?"
"Yeppers. It's the 538th element. Took me a hike to find it."
"Well I wanted to do something with it."
"Then go get it. I'm telling you, it'll take exactly 538 steps."


Andrei