For a simple hello world program in D,
imports are needed.
import statement makes all public functions
and types from the given module available.
The standard library, called Phobos,
is located under the package
and its modules are referenced through
import statement can also be used to selectively
import certain symbols of a module:
import std.stdio: writeln, writefln;
Selective imports can be used to improve readability by making it obvious where a symbol comes from, and also as a way to prevent clashing of symbols with the same name from different modules.
import statement does not need to appear at the top of a source file.
It can also be used locally within functions or any other scope.