Program structure

D is a compiled systems language with C-like syntax, garbage collection by default, and fast compile times. Its standard library is Phobos, and its runtime is druntime.

Every program starts at void main() (or int main(string[] args) to read arguments and return an exit code).

import std.stdio; brings in writeln (prints its arguments then a newline), write (no newline), and writefln (printf-style formatting).

Three compilers share one frontend: dmd (the reference compiler, fastest builds), ldc2 (LLVM backend, well-optimized code), and gdc (GCC backend). dmd -run app.d compiles and runs in one step, and rdmd app.d does the same with caching.

writeln takes any number of arguments of any type and prints them with no separator: writeln("x = ", 3) prints x = 3.

Comments are // to end of line, /* ... */, and /+ ... +/, which nests, so you can comment out a block that already contains comments.

import std.stdio;

void main(string[] args)
{
    writeln("Hello, D");
    write("no newline, ");
    writeln("then one");
    writeln("args: ", args.length, ", answer = ", 6 * 7);
    writefln("%s is %d years old", "D", 2026 - 2001);
    /+ nested /* comments */ are fine +/
}