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
