Hm, but why can't static assert provide an instantiation trace? I
can live without error message but duplicating same condition
twice (one time being part of implementation) hurts my eyes :(
On Monday, 21 January 2013 at 17:16:22 UTC, Ali Çehreli wrote:
On 01/21/2013 08:32 AM, mist wrote:
> phobos style
> guidelines favor constraints heavily over static asserts but
this
> exactly the example when I am uneasy about such choice:
static assert
> can both provide more user-friendly error message here and
remove some
> code duplication.
Agreed but there is a problem with 'static assert' in the
implementation: We don't know what user code has caused the
issue. (It is a common problem in C++ templated libraries that
a hard-to-understand compilation error is produced from inside
a library function template.)
D's template constraints move the compilation error to the
exact place of the user code.
void foo(string s)()
if ((s == "hello") || (s == "goodbye"))
{
// ...
}
void main()
{
foo!"howdy"(); // <-- compilation error on this line
}
It is better:
Error: template instance foo!("howdy") foo!("howdy") does not
match template declaration foo(string s)() if (s == "hello" ||
s == "goodbye")
To be honest, it is kind of obvious in this simple case but
sometimes the cause of the error is still hard to understand
even with template consraints.
Ali
