Convert duration to years?

[rikki cattermole via Digitalmars-d-learn]

On 15/01/2017 4:43 PM, Nestor wrote:
> Hi,
>
> I would simply like to get someone's age, but I am a little lost with
> time and date functions. I can already get the duration, but after
> reading the documentation it's unclear to me how to convert that into
> years. See following code:
>
> import std.stdio;
>
> void getAge(int yyyy, int mm, int dd) {
>   import std.datetime;
>   SysTime t1 = SysTime(Date(yyyy, mm, dd));
>   SysTime t2 = Clock.currTime();
>   writeln(t2 - t1);
> }
>
> int main() {
>   try
>     getAge(1980, 1, 1);
>   catch(Exception e) {
>     writefln("%s.\n(%s, line %s)", e.msg, e.file, e.line);
>   }
> }
>
> Notice getAge should return ubyte instead of void, only I haven't been
> able to find how to do it. Any suggestion would be welcome.
>
> Thanks in advance.

So I had a go at this and found I struggled looking at "magic" functions 
and methods.
Turns out there is a much simpler answer.

int getAge(int yyyy, int mm, int dd) {
   import std.datetime;
   auto t1 = cast(DateTime)SysTime(Date(yyyy, mm, dd));
   auto t2 = cast(DateTime)Clock.currTime();

   int numYears;
   while(t2 > t1) {
      t1.add!"years"(1);
      numYears++;
   }

   return numYears;
}