assert vs. enforce in Phobos code

[Joseph Rushton Wakeling]

Hello all,

This is a subject I think we've visited before, but I can't find the old 
discussion threads :-(

As some of you know I'm working on a successor to std.random -- it's been put on 
hold the last 8 weeks or so by country/life/work changes, but now I'm back onto 
it.  One of the things I'm examining in the course of that is the error checking.

For example, a call to uniform(a, b) sees the function ensure that the interval 
is appropriate via an enforce(a <= b).  The result is that passing the wrong 
values to uniform() will bring your program down.  There are many other 
comparable cases in the module.

Part of me feels this is absolutely right and that such errors should be 
strictly objected to in this way.  On the other hand, this seems a wrong 
approach given that these kinds of functions are surely going to be called deep 
within the program -- we're not verifying user input here, it would be a logical 
error in the program to pass wrong bounds to uniform() and so on.

My inclination is to clean this stuff up, to generally replace enforce's with 
asserts, to provide in- and out-contracts where appropriate, and so on.

Thoughts, remarks, ... ?

Thanks & best wishes,

      -- Joe