Why file.exists of relative path on Linux always return false?

[Suliman via Digitalmars-d-learn]

I am trying to check relative path on Linux for exists.
import std.stdio;
import std.path;
import std.file;
import std.string;



string mypath = "~/Documents/imgs";

void main()
{
 if(!mypath.exists)
        {
                writeln(mypath, " do not exists");            
        }

 if(!mypath.exists)
        {
                writeln(mypath, " do not exists");            
        }

 if("/home/dima/Documents/imgs".exists)
        {
                writeln("/home/dima/Documents/imgs");
                writeln("Dir exists");
        }

}

~/Documents/imgs always return "do not exists". But full path: 
"/home/dima/Documents/imgs" is "Dir exists".

Why? It's same paths!