Compile-time vs. compile-time

Introduction

One of D's oft-touted features is its awesome compile-time capabilities, which open up wonderful meta-programming opportunities, code-generation techniques, compile-time introspection, DSLs that are transformed into code at compile-time and therefore incur zero runtime overhead, and plenty more.

However, said "compile-time" capabilities are also often the source of much confusion and misunderstanding, especially on the part of newcomers to D, often taking the form of questions posted to the discussion forum by frustrated users, such as: "Why doesn't the compiler let me do this?!", "Why doesn't this do what I think it should do?", "Why can't the compiler figure this simple thing out?! The compiler is so stupid!", and so on.

This article hopes to clear up most of these misunderstandings by explaining just what exactly D's "compile-time" capabilities are, give a brief overview of how it works, and hopefully thereby give newcomers to D a better handle on what exactly can be done, and what to do when you run into a snag.