templated isNaN

[Paolo Invernizzi]

Someone can suggest me a convenient way to declare an 'isNaN' 
templated function that plays well with the 'standard.math.isNaN'?

The target is to be able to define isNaN functions for my custom 
structures, and I want to keep the same name...

---
import std.math;

bool isNaN(T)(T t) if(is(T==string)){ return true; }

// that is really necessary? What if I have my isNaN in different 
modules? Must duplicate?
// bool isNaN(T)(T t) if(is(T:real)) { return std.math.isNaN(t); }

void foo(){
	bool b = isNaN(0.0);
}

/d471/f783.d(9): Error: template f783.isNaN does not match any 
function template declaration. Candidates are:
/d471/f783.d(3):        f783.isNaN(T)(T t) if (is(T == string))
/d471/f783.d(9): Error: template f783.isNaN(T)(T t) if (is(T == 
string)) cannot deduce template function from argument types 
!()(double)
---

Thanks in advance!

- Paolo Invernizzi