[phobos] Drought of functions that throw exceptions

[Richard Palme]

On Thursday, 1 November 2018 at 08:42:28 UTC, Don Clugston wrote:
> Absolutely there is a reason. Exceptions are very expensive, 
> especially in low-level functions.

Then I got a few follow-up questions (I hope this isn't the wrong 
place for beginner questions):
1. Why is it that arrays throw RangeExceptions? Shouldn't that be 
too costly too?
2. I might be wrong but I thought that in the following code 
example the additional cost is only the cost of one additional 
branch from the if statement, unless of course i >= length which 
should never happen.

if (i < length)
{
     //do something
}
else
{
     throw new Exception();
}


3. When exceptions can't be used, then I guess the best way to 
ensure safety are pre and post contracts. But I actually don't 
know how to activate the contracts in phobos.
I thought that maybe I have to build both phobos and dmd with

$make -f posix.mak -j8 BUILD=debug

but I just tried that and I don't think it worked.