Safety/purity and assert/enforce error messages

[Jonathan M Davis]

On Thursday, September 12, 2013 12:42:34 H. S. Teoh wrote:
> On Thu, Sep 12, 2013 at 09:12:18PM +0200, bearophile wrote:
> > H. S. Teoh:
> > >In phobos git HEAD, std.format has been made pure @safe nothrow (and
> > >
> > >CTFE-able), so you should be able to write your assert as:
> > > assert(condition, format("x = %s, blahblah", x));
> > 
> > With the latest DMD from updated GIT head:
> > 
> > 
> > import std.string: format;
> > void main() pure nothrow {
> > 
> > string x = "hello";
> > bool condition = true;
> > assert(condition, format("x = %s, blahblah", x));
> > 
> > }
> > 
> > 
> > It gives:
> > 
> > test.d(5): Error: 'std.string.format!(char, string).format' is not nothrow
> > test.d(2): Error: function 'D main' is nothrow yet may throw
> 
> [...]
> 
> Oops. Apparently I wrote nothrow but forgot to test it. I did test pure
> and @safe, though, so at least those two should work.

format can't be nothrow, because it throws when you screw up the format 
specifiers. You have to wrap it in a try-catch block and assert(0) in the catch 
block if you want to put it in a nothrow function. std.datetime does this in 
at least a few places.

- Jonathan M Davis