On 01/21/2013 10:02 AM, mist wrote:
> Hm, but why can't static assert provide an instantiation trace? I can
> live without error message
I forgot to mention that template constraints take part in choosing the
implementation as well:
void foo(string s)()
if ((s == "hello") || (s == "goodbye"))
{
// ...
}
void foo(string s)()
if (s == "howdy")
{
// ...
}
void main()
{
foo!"howdy"(); // not an error: goes to special implementation
foo!"merhaba"(); // error: no implementation at all
}
In order to achieve the same goal without template constraints we have
two options:
1) Template specialization, which I don't think is not valid for
non-type template parameters like string:
void foo(string s == "hello")() // ERROR; I don't think possible
{
// ...
}
2) 'static if' in the implementation:
void foo(string s)()
{
static if ((s == "hello") || (s == "goodbye")) {
// ...
} else static if (s == "howdy") {
// ...
} else {
static assert(false, "Invalid string " ~ s);
}
}
void main()
{
foo!"howdy"();
foo!"merhaba"();
}
You are right though, dmd does produce useful information for this
simple case:
Error: static assert "Invalid string merhaba"
instantiated from here: foo!("merhaba")
The only shortcoming that I see in this case is that the implementations
for different string values are inside the same function template.
> but duplicating same condition twice (one
> time being part of implementation) hurts my eyes :(
Can you elaborate. I don't see the duplication.
Ali
