handson-dlang/hands-on_dlang.md

# Hands-On DLang

## Setup

### Installing DMD and DUB

#### OS X

##### Installing with Homebrew (recommended)

```bash
brew install dmd
brew install dub
```

##### Installing locally using the install script

```bash
curl -fsS https://dlang.org/install.sh | bash -s dmd
echo "~/.dlang/dmd-2.079.0/activate" >> ~/.profile # Add dmd and dub to PATH on starting a bash shell
```

##### Installing using the installer

* Download http://downloads.dlang.org/releases/2.x/2.079.0/dmd.2.079.0.dmg.
* Open `dmd.2.079.0.dmg`
* Run `DMD2.pkg` (you might need to activate the “allow installing applications from unverified developers” option in your security settings) and install with the default settings.

#### Windows

* Download http://downloads.dlang.org/releases/2.x/2.079.0/dmd-2.079.0.exe.
* Run `dmd-2.079.0.exe` and install with the default settings (this will also install Visual Studio if you do not have it installed yet).

### Recommended editor setup

Visual Studio Code is the recommended editor, because it has the best D integration at the moment.
If you want to use another editor or IDE, that is perfectly fine.
However, instructions will only be provided for Visual Studio Code.

#### Installation of Visual Studio Code

Download and install Visual Studio Code from here: https://code.visualstudio.com/. OS X users can also install it using Homebrew:

```bash
brew tap caskroom/cask
brew cask install visual-studio-code
```

#### Extension setup

* Open the Extension view in the sidebar:
  |Operating system|Shortcut |
  |----------------|---------|
  |OS X |⌘ + ⇧ + X|
  |Windows |⌃ + ⇧ + X|
* Install the extension “D Programming Language (code-d)” (requires that git is installed).
* Restart Visual Studio Code.

## Basics

### Hello World

```D
import std.stdio;

void main() {
    writeln("Hello World");
}
```

### Imports and modules

D has the concept of _modules_ and _packages_.
By importing a certain module with the `import` statement, all public symbols from module become available.
The standard library, called Phobos, is located in the `std` package.
E.g. in order to import the `file` module from Phobos, you would write:

```D
import std.file;
```

#### Selective imports

It is possible (and often good style) to import symbols selectively from a module:

```D
import std.stdio: writeln, writefln;
```

#### Scoped imports

It is not necessary to place imports at the beginning of a file.
They can be located anywhere in the code.
If they appear inside a certain scope (delimited by braces), the imported symbols are only available inside that scope.
Here is an alternative version of the hello world program:

```D
void main()
{
import std.stdio: writeln;
writeln("Hello World");
}
/* writeln is not available outside of the main function */
```

#### Imports match files and directories

The module system is entirely based on files.
E.g. `my.thing` refers to a file `thing.d` in the folder `my/`.

### Basic Types

D has the following basic types:

| Datatypes                       | Size                                                         |
| ------------------------------- | ------------------------------------------------------------ |
| `bool` `byte`, `ubyte`, `char`  | 8-bit                                                        |
| `short`, `ushort`, `wchar`      | 16-bit                                                       |
| `int`, `uint`, `dchar`, `float` | 32-bit                                                       |
| `long`, `ulong`, `double`       | 64-bit                                                       |
| `real`                          | >= 64-bit (generally 64-bit, but 80-bit on Intel x86 32-bit) |

`char` represents UTF-8 characters, `wchar`represents UTF-16 characters, and `dchar` represents UTF-32 characters.

#### Type conversion

For integer types, automatic type conversion is only allowed if no precision is lost (e.g. `int` to `long`).
All conversion between floating point types are allowed (e.g. `double` to `float`).

Manual type conversion is achieved with the `cast` expression:

```D
long a = 1;
int b = cast(int) a;
```

#### Type properties

All types have a property `.init` to which variables of that type are initialized, if they are not initialized explicitly.
For integer types, this is `0` and for floating point types it is `nan`.

Every type also has a `.stringof` property which yields its name as a string.

Integer types have some more properties:

| Property | Description                         |
| -------- | ----------------------------------- |
| `.max`   | The maximum value the type can hold |
| `.min`   | The minimum value the type can hold |

And so do floating point types:

| Property      | Description                                                 |
| ------------- | ----------------------------------------------------------- |
| `.max`        | The maximum value the type can hold                         |
| `.min_normal` | The smallest representable normalized value that is not `0` |
| `.nan`        | NaN value                                                   |
| `.infinity`   | Infinity value                                              |
| `.dig`        | number of decimal digits of precisions                      |
| `.mant_dig`   | number of bits in mantissa                                  |
| …             |                                                             |

#### Indexing

For indexing, usually the alias type `size_t` is used, which is large enough to represent an offset into all addressable memory.

### Variable declarations

Variables are declared by writing the type followed by the variable name:

```D
int myVar;
```

They can also be explicitly initialized:

```D
int myVar = 42;
```

It is also possible to declare several variables at once:

```D
int myVar, someOtherVar;
```

D has automatic type deduction, so when explicitly initializing a variable, it is not necessary to mention the type.
Instead we can use the `auto` keyword:

```D
auto myVar = 42;
```

Here is a combination of the above notations:

```D
auto myInt = 42, myFloat = 4.2f;
```

### Functions

The basic syntax for functions is very similar to C:

```D
int add(int lhs, int rhs) {
    return lhs + rhs;
}
```

#### Return type deduction

A functions return type can be defined to be `auto`.
In this case, the return type will be infered.
Multiple return statements are possible, but must return compatible types.

```D
auto add(int lhs, int rhs) { // returns `int`
    return lhs + rhs;
}

auto lessOrEqual(int lhs, int rhs) { // returns `double`
    if (lhs <= rhs)
        return 0;
    else
        return 1.0;
}
```

#### Default arguments

Those also work the same as in C and other languages:

```D
void plot(string msg, string color = "red") {
    /* ... */
}
plot("D rocks");
plot("D rocks", "blue");
```

#### Local functions

It is possible to define functions locally (even inside other functions).
Those functions are not visible outside their parents scope.

```D
void fun() {
    int local = 10;
    int fun_secret() {
        local++; // that's legal
    }
    /* … */
}
static assert(!__traits(compiles, fun_secret())); // fun_secret is not visible here
```

### Control flow

#### if…else

Very similar to how it is defined in other languages:

```D
if (a == 5) {
    writeln("Condition is met");
} else if (a > 10) {
    writeln("Another condition is met");
} else {
    writeln("Nothing is met!");
}
```

#### switch…case

Also very similar to how it is defined in other languages, but for it works for integer types, bools and strings (which will be covered later).

```D
string myString;
/* … */
switch(myString) {
    case "foo":
        writeln(`Cool, myString was "foo"`);
        break;
    default:
        writeln("Meh, myString was something boring");
        break;
}
```

For integer types, it is also possible to define ranges:

```D
int c = 5;
switch(c) {
    case 0: .. case 9:
        writeln(c, " is within 0-9");
        break; // necessary!
    case 10:
        writeln("A Ten!");
        break;
    default: // if nothing else matches
        writeln("Nothing");
        break;
}
```

#### Loops

`while`-, `do`…`while`- and classical `for`-loops all work the same as in C++/Java etc.

##### Breaking out of outer loops

As usual, you can break out of a loop immediately by using the `break` keyword. Additionally, you can also break out of outer loops by using labels:

```D
outer:
for (int i = 0; i < 10; ++i) {
    for (int j = 0; j < 5; ++j) {
        /* … */
        break outer; // breaks out of the outer loop
    }
}
```