On 07/03/18 17:11, Steven Schveighoffer wrote:
Well, you could do it with templates, but obviously that is less desirable:
void func2(Args...)(Args args) if(is(typeof(func(args)))) { return
func(args); }
I never understood why anyone would use "is" for checking compilability
when we have "__triats(compiles, func(args))".
With that aside, I would urge you not to use this test. It makes the
error case worse. Check this out:
void func1(int a) {
}
void func2(Args...)(Args args) if( __traits(compiles, func1(args))) {
func1(args);
}
void func3(Args...)(Args args) {
func1(args);
}
void main() {
long var;
func2(var);
func3(var);
}
Which error would you rather get? Calling func2 results in:
test.d(15): Error: template test.func2 cannot deduce function from
argument types !()(long), candidates are:
test.d(4): test.func2(Args...)(Args args) if (__traits(compiles,
func1(args)))
Calling func3 results in:
test.d(9): Error: function test.func1(int a) is not callable using
argument types (long)
test.d(9): cannot pass argument _param_0 of type long to
parameter int a
test.d(16): Error: template instance `test.func3!long` error instantiating
When calling func3, the compiler is telling you what's wrong (i.e. - you
are passing a long to a function expecting a var). When calling func2,
all you know is that there is some problem.
With that out of the way, I don't like generating proxy functions with
"Args..." templates. They generate unneeded code bloat:
void main() {
int var1;
ubyte var2;
byte var3;
ushort var4;
short var5;
uint var6;
// This generates 6 instantiations of the same function
func2(var1);
func2(var2);
func2(var3);
func2(var4);
func2(var5);
func2(var6);
}
If I could use Params, there would be only one instantiation.
