Checking function parameters in Phobos

[Jacob Carlborg]

On 2013-11-20 01:01, Andrei Alexandrescu wrote:
> There's been recent discussion herein about what parameter validation
> method would be best for Phobos to adhere to.
>
> Currently we are using a mix of approaches:
>
> 1. Some functions enforce()
>
> 2. Some functions just assert()
>
> 3. Some (fewer I think) functions assert(0)
>
> 4. Some functions don't do explicit checking, relying instead on
> lower-level enforcement such as null dereference and bounds checking to
> ensure safety.
>
> Each method has its place. The question is what guidelines we put
> forward for Phobos code to follow; we're a bit loose about that right now.
>
> A second, just as interesting topic, is how to design abstractions for
> speed and safety. There are cases in which spurious checking is
> prohibitively expensive if not necessary, so it should be avoided where
> necessary. Examples:
>
> (a) FracSecs(long x) validates x to be within range. The cost of the
> validation itself is about as high as the payload itself (which is one
> assignment).
>
> (b) sort() offers a SortedRange with its goodies. We also have
> assumeSorted that also offers a SortedRange, but relies on the user to
> validate that assumption.
>
> (c) A variety of text functions currently suffer because we don't make
> the difference between validated UTF strings and potentially invalid ones.
>
> Walter and I are thinking of fostering the idiom in which types (or
> attributes?) are used as information about validation, similar to how
> assumeSorted works. Building on that, we'd have a function like "static
> FracSecs assumeValid(long)" inside FracSecs (no need for a different
> type here). Then, we'd have a CleanUTF type or something that would
> guarantee the string stored within has been validated.

Would we accompany the assumeSorted with an assert in the function 
assuming something is sorted? We probably don't want to rely on convention.

What about distributing a version of druntime and Phobos with asserts 
enabled that is used by default (or with the -debug flag). Then a 
version with asserts disabled is used when the -release flag is used.

We probably also want it to be possible to use Phobos with asserts 
enabled even in release mode.

-- 
/Jacob Carlborg