how to pass a variable name in the template in this case?

[Zhenya]

module main;

import std.stdio;

immutable double f = 0;

template T(alias a)
{
        auto T = a;
}

int main(string[] argv)
{
        char f = 'a';
        writeln(typeid(T!f));//deduce f as 'a'
        readln();
        return 0;
}