Why does File.byLine() return char[] and not string

[Shriramana Sharma via Digitalmars-d-learn]

Is there a particular reason that File.byLine() returns char[] and not 
string i.e. immutable(char)[]? Is it just to avoid being overly restrictive? 
It seems that having to .idup it is inefficient...

-- 
Shriramana Sharma, Penguin #395953