"Try it now"

[Jonathan M Davis]

> On Thu, 14 Apr 2011 13:16:33 -0400, Andrei Alexandrescu
> 
> <SeeWebsiteForEmail at erdani.org> wrote:
> > On 4/14/11 12:00 PM, Steven Schveighoffer wrote:
> >> On Thu, 14 Apr 2011 12:48:26 -0400, Andrei Alexandrescu
> >> 
> >> <SeeWebsiteForEmail at erdani.org> wrote:
> >>> On 4/14/11 9:03 AM, Steven Schveighoffer wrote:
> >>>> Sometimes, I worry that my unit tests or asserts aren't running. Every
> >>>> once in a while, I have to change one to fail to make sure that code
> >>>> is
> >>>> compiling (this is especially true when I'm doing version statements
> >>>> or
> >>>> templates). It would be nice if there was a -assertprint mode which
> >>>> showed asserts actually running (only for the module compiled with
> >>>> that
> >>>> switch, of course).
> >>> 
> >>> Could this be achieved within the language?
> >> 
> >> I think you need to do it at the compiler level to make it useful. For
> >> example, an assert like:
> >> 
> >> assert(container.length == 5);
> >> 
> >> To print this out properly, I'd want to see that the assert passed, but
> >> also what the test was.
> > 
> > What's needed here is a "text of expression" feature similar to C's "#".
> > That would help enforce and other artifacts too. I'm thinking along the
> > lines of:
> > 
> > void myassert(string expr = __traits(text, condition))(bool condition) {
> > 
> > ...
> > 
> > }
> > 
> > with, of course, a simpler syntax.
> 
> It still isn't exactly right. Assert has some special properties that
> cannot be duplicated exactly with library code. Such as true lazy
> evaluation and elimination during release mode.
> 
> But yes, it would be nice to be able to get a string of the parameters of
> a function (macro?). It would certainly make this more feasible.
> 
> However, all this is ignoring one simple thing -- the hundreds of
> thousands of lines of code (mostly from std.datetime ;) ) that already
> have asserts. Hooking assert directly automatically gives us a tool for
> printf debugging without changing any code.

Actually, std.datetime doesn't use assert much. It mostly uses a version of 
assertPred which it has as a private function. Also, I've been rewriting the 
unit tests, and that will result in far fewer actual lines with assert or 
_assertPred thanks to more looping and whatnot. It does increase the need for 
printing out the actual results from an assertion though (which _assertPred 
does on failure). And what you're asking for here is at least related to the 
requested improvements to assert which resulted in assertPred being scrapped.

- Jonathan M Davis