Book Image

Crystal Programming

By : George Dietrich, Guilherme Bernal
Book Image

Crystal Programming

By: George Dietrich, Guilherme Bernal

Overview of this book

Crystal is a programming language with a concise and user-friendly syntax, along with a seamless system and a performant core, reaching C-like speed. This book will help you gain a deep understanding of the fundamental concepts of Crystal and show you how to apply them to create various types of applications. This book comes packed with step-by-step explanations of essential concepts and practical examples. You'll learn how to use Crystal’s features to create complex and organized projects relying on OOP and its most common design patterns. As you progress, you'll gain a solid understanding of both the basic and advanced features of Crystal. This will enable you to build any application, including command-line interface (CLI) programs and web applications using IOs, concurrency and C bindings, HTTP servers, and the JSON API. By the end of this programming book, you’ll be equipped with the skills you need to use Crystal programming for building and understanding any application you come across.
Table of Contents (26 chapters)
1
Part 1: Getting Started
5
Part 2: Learning by Doing – CLI
10
Part 3: Learn by Doing – Web Application
13
Part 4: Metaprogramming
18
Part 5: Supporting Tools

Iterating methods

Iterating methods have a lot in common with iterating types, just with a different macro type. The first thing we need in order to iterate over methods is TypeNode, representing the type whose methods we are interested in. From there, we can call the #methods method, which returns ArrayLiteral(Def) of all the methods defined on that type. For example, let's print an array of all the method names within a class:

abstract class Foo
  def foo; end
end
 
module Bar
  def bar; end
end
class Baz < Foo
  include Bar
  def baz; end
  def foo(value : Int32); end
  def foo(value : String); end
  def bar(x); end
end
baz = Baz.new
baz.bar 1
baz.bar false
{{pp Baz.methods.map &.name}}

Running this would output the following:

[baz, foo, foo, bar]

Notice that similar to the #includers method, only methods explicitly defined within the type are printed. Also notice that the #foo method is...