The evils of __traits(compiles)

[Paul Backus]

On Thursday, 21 January 2021 at 20:27:36 UTC, H. S. Teoh wrote:
> Unfortunately, my PR touches one of the functions used by 
> setHandler. A typo caused a compile error inside setHandler 
> itself, but since __traits(compiles) does not distinguish 
> between errors caused by the candidate method and errors inside 
> setHandler itself, the erroneous code simply caused *all* 
> methods to be skipped -- silently.  The problem would not be 
> noticed until runtime when some methods mysteriously go 
> missing. :-(

This seems like a bug that would have been easily caught by a 
unit test for setHandler.

Remember: the compiler does not check your templates until you 
actually try to instantiate them. If you want to be sure that 
they instantiate correctly, you have to test them.