add section about templates
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# Hands-On DLang
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- [Hands-On DLang](#hands-on-dlang)
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- [Setup](#setup)
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- [Installing DMD and DUB](#installing-dmd-and-dub)
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- [OS X](#os-x)
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- [Installing with Homebrew (recommended)](#installing-with-homebrew-recommended)
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- [Installing locally using the install script](#installing-locally-using-the-install-script)
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- [Installing using the installer](#installing-using-the-installer)
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- [Windows](#windows)
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- [Recommended editor setup](#recommended-editor-setup)
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- [Installation of Visual Studio Code](#installation-of-visual-studio-code)
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- [Extension setup](#extension-setup)
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- [Basics](#basics)
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- [Hello World](#hello-world)
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- [Imports and modules](#imports-and-modules)
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- [Selective imports](#selective-imports)
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- [Scoped imports](#scoped-imports)
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- [Imports match files and directories](#imports-match-files-and-directories)
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- [Basic Types](#basic-types)
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- [Type conversion](#type-conversion)
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- [Type properties](#type-properties)
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- [Indexing](#indexing)
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- [Variable declarations](#variable-declarations)
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- [Mutability](#mutability)
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- [`immutable`](#immutable)
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- [`const`](#const)
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- [Functions](#functions)
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- [Return type deduction](#return-type-deduction)
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- [Default arguments](#default-arguments)
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- [Local functions](#local-functions)
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- [Memory and pointers](#memory-and-pointers)
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- [Memory safety](#memory-safety)
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- [Structs](#structs)
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- [Member functions](#member-functions)
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- [`const` member functions](#const-member-functions)
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- [`static` member functions](#static-member-functions)
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- [Arrays](#arrays)
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- [Static arrays](#static-arrays)
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- [Dynamic arrays](#dynamic-arrays)
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- [Array operations and properties](#array-operations-and-properties)
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- [Slices](#slices)
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- [Alias and `string`s](#alias-and-strings)
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- [Control flow](#control-flow)
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- [if…else](#if%E2%80%A6else)
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- [switch…case](#switch%E2%80%A6case)
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- [Old fashioned loops](#old-fashioned-loops)
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- [Breaking out of outer loops](#breaking-out-of-outer-loops)
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- [`foreach` loops](#foreach-loops)
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- [Element iteration](#element-iteration)
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- [Access by reference](#access-by-reference)
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- [Iterate `n` times](#iterate-n-times)
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- [Iteration with index counter](#iteration-with-index-counter)
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- [Ranges](#ranges)
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- [Laziness](#laziness)
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- [Copying ranges](#copying-ranges)
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- [`RandomAccessRange`s](#randomaccessranges)
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- [Lazy range algorithms](#lazy-range-algorithms)
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- [Associative arrays](#associative-arrays)
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- [Classes](#classes)
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- [Inheritance](#inheritance)
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- [Final and abstract member functions](#final-and-abstract-member-functions)
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- [Checking for identity](#checking-for-identity)
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- [Interfaces](#interfaces)
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- [Templates](#templates)
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- [Template functions](#template-functions)
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- [Other templates](#other-templates)
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- [Template value parameters](#template-value-parameters)
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- [Other template parameters](#other-template-parameters)
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## Setup
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### Installing DMD and DUB
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@ -794,3 +862,144 @@ if (c == null) // error
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if (c is null) // ok
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/* … */
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```
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### Interfaces
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`interface`s work basically the same as in Java:
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```D
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interface Animal {
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void makeNoise();
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}
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class Dog : Animal {
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override void makeNoise() {
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writeln('woof!');
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}
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}
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auto dog = new Dog;
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Animal animal = dog; // implicit cast to interface
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animal.makeNoise();
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```
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### Templates
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#### Template functions
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Template functions in D are very similar to C++ template functions:
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```D
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auto add(T)(T lhs, T rhs) {
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return lhs + rhs;
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}
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add!int(5,10);
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add!float(5.0f, 10.0f);
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add!Animal(dog, cat); // error, Animal does not implement +
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```
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In the explicit template notation, the `add` template function would look like
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this:
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```D
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template add(T) {
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auto add(T lhs, T rhs) {
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return lhs + rhs;
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}
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}
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```
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D also allows implicit function template instanciation:
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```D
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add(5, 10); // same as add!int(5,10)
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```
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Templates can have more than one template parameter:
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```D
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void print(S, T)(S x, T y) {
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writeln(x);
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writeln(y);
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}
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print!(int, string)(42, "is the best number");
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```
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#### Other templates
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Of course, `struct`s, `class`es and `interface`s can also be templated:
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```D
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struct S(T) {
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/* … */
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}
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auto s = S!int;
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```
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It is also possible to have variable templates:
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```D
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ubyte[T.sizeof * 8] buffer8(T) = 42;
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auto myBuffer = buffer!(int, 8); // create a buffer with space for 8 ints and initialize its elements to 42
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static assert(is(typeof(myBuffer) == ubyte[32]));
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assert(myBuffer[0] == 42);
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```
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This gets lowered to the following explicit template syntax:
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```D
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template buffer8(T) {
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ubyte[T.sizeof * 8] buffer8 = 42;
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}
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```
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#### Template value parameters
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So far we have only seen templateF type parameters. It is also possible to have
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template value parameters:
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```D
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struct Animal(string noise) {
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void makeNoise() {
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writeln(noise);
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}
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}
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auto dog = Animal!"woof!"();
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dog.makeNoise(); // woof!
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```
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#### Other template parameters
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There are some other types of template parameters: template alias parameters
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and template sequence parameters. Template alias parameters can be any D symbol
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(which means basically anything except for basic types):
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```D
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void print(alias var)() {
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writeln(var);
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}
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struct S {}
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auto x = 42;
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print!x();
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print!4.2f();
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print!"foo"();
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print!S(); // error, would be actually legal, but cant pass types to writeln
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```
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Template sequence parameters take a variadic number of template arguments:
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```D
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void print(Args...)(Args args) {
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foreach (arg; args) { // yes, we can iterate over them (loop unrolling)
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writeln(arg);
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}
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}
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print(42, 3.5f, "foo");
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print(); // also valid, prints nothing
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```
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