learnxinyminutes-docs/vala.html.markdown
2017-08-25 12:26:44 -04:00

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---
language: vala
contributors:
- ["Milo Gilad", "https://github.com/Myl0g"]
filename: LearnVala.vala
---
In GNOME's own words, "Vala is a programming language that aims to bring modern programming language features to GNOME developers without imposing any additional runtime requirements and without using a different ABI compared to applications and libraries written in C."
Vala has aspects of Java and C#, so it'll be natural to those who know either.
[Read more here.](https://wiki.gnome.org/Projects/Vala)
```vala
// Single line comment
/* Multiline
Comment */
/**
* Documentation comment
*/
/* Data Types */
char character = 'a'
unichar unicode_character = 'u' // 32-bit unicode character
int i = 2; // ints can also have guaranteed sizes (e.g. int64, uint64)
uint j = -6; // Won't compile; unsigned ints can only be positive
long k;
short l;
ushort m;
string text = "Hello,"; // Note that the == operator will check string content
string verbatim = """This is a verbatim (a.k.a. raw) string. Special characters
(e.g. \n and "") are not interpreted. They may also be multiple lines long.""";
// String Templates allow for easy string formatting
string string_template = @"$text world"; // "$text" evaluates to "Hello,"
int test = 5;
int test2 = 10;
string template2 = @"$(test * test2) is a number."; // Expression evaluation
string template_slice = string_template[7:12]; // => "world"
// Most data types have methods for parsing.
bool parse_bool = bool.parse("false"); // => false
int parse_int = int.parse("-52"); // => -52
string parse_string = parse_int.to_string(); // => "-52"
/* Basic I/O */
stdout.printf(parse_string); // Prints to console
string input = stdin.read_line(); // Gets input from console
stderr.printf("Error message"); // Error printing
/* Arrays */
int[] int_array = new int[10]; // Array of ints with 10 slots
int better_int_array[10]; // Above expression, shortened
int_array.length; // => 10;
int[] int_array2 = {5, 10, 15, 20}; // Can be created on-the-fly
int[] array_slice = int_array2[1:3]; // Slice (copy of data)
unowned int[] array_slice_ref = int_array2[1:3]; // Reference to data
// Multi-dimensional Arrays (defined with a number of commas in the brackets)
int[,] multi_array = new int[6,4]; // 6 is the number of arrays, 4 is their size
int[,] multi_array2 = {{7, 4, 6, 4},
{3, 2, 4, 6},
{5, 9, 5, 1}}; // new int[3,4]
multi_array2[2,3] = 12; // 2 is the array, 3 is the index in the array
int first_d = multi_array2.length[0] // => 3
int second_d = multi_array2.length[1] // => 4
// Stacked arrays (e.g. int[][]) where array lengths vary are not supported.
// Multi-dimensional arrays cannot be sliced, nor can they be converted to one-
// dimensional.
int[] add_to_array = {};
add_to_array += 12; // Arrays can be dynamically added to
add_to_array.resize(20); // Array now has 20 slots
uint8[] chars = "test message".data;
chars.move(5, 0, 7);
stdout.printf((string) chars); // Casts the array to a string and prints it
/* Control Flow */
int a = 1;
int b = 2;
int[] foreach_demo = {2, 4, 6, 8};
while (b > a) { // While loop; checks if expression is true before executing
b--;
}
do {
b--;
}
while (b > a); // Do While loop; executes the code in "do" before while (b > a)
for (a = 0; a < 10; a++) { stdout.printf("%d\n", a); } // for loop
foreach (int foreach_demo_var in foreach_demo) {
stdout.printf("%d\n", foreach_demo_var);
} // foreach works on any iterable collection
if (a == 0) {
break;
} else if (a > 1) {
stdout.printf("%d\n", a);
} else {
break;
} // if-then-else
switch (a) {
case 1:
stdout.printf("A is 1\n");
break;
case 5:
case 10:
stdout.printf("A is 5 or 10\n");
break;
default:
stdout.printf("???\n")
break;
} // switch statement
/* Type Casting and Inference */
int cast_to_float = 10;
float casted_float = (float) cast_to_float; // static casting; no runtime checks
// For runtime checks, use dynamic casting.
// Dynamically casted objects must be the following:
// - Object's class is the same class as the desired type
// - Object's class is a subclass of the desired type
// - Desired class is an interface implemented by the object's class
float dyna_casted_float = cast_to_float as float // Won't compile
var inferred_string = "hello"; // Type inference
/* Methods (a.k.a. functions) */
int method_demo(string arg1, Object arg2) { // Returns int and takes args
return 1;
}
// Vala methods cannot be overloaded.
void some_method(string text) { }
void some_method(int number) { } // Won't compile
// To achieve similar functionality, use default argument values.
void some_better_method(string text, int number = 0) { }
some_better_method("text");
some_better_method("text", 12);
// varargs (variable-length argument lists) are also supported.
void method_with_varargs(int arg1, ...) {
var varargs_list = va_list(); // gets the varargs list
string arg_string = varargs_list.arg(); // gets arguments, one after another
int int_vararg = varargs_list.arg();
stdout.printf("%s, %d\n", arg_string, int_vararg)
}
string? ok_to_be_null(int? test_int) { } // "?" denotes possible null value
// Delegates
delegate void DelegateDemo(char char_a);
void delegate_match(char char_a) { // Matches the delegate's signature
stdout.printf("%d\n");
}
void call_delegate(DelegateDemo d, char char_b) { // Takes a delegate arg
d(char_b) // calls delegate
}
void final_delegate_demo() {
call_delegate(delegate_match); // Passes matching method as argument
}
// Lambdas (a.k.a. Anonymous Methods) are defined with "=>"
(a) => { stdout.printf("%d\n", a); } // Prints "a"
/* Namespaces */
namespace NamespaceDemo {
// Allows you to organize variable names
int namespace_int = 12;
}
namespace_int += 5; // Won't compile
using NamespaceDemo;
namespace_int += 5; // Valid
/* Structs and Enums */
struct Closet {
public uint shirts; // Default access modifier is private
public uint jackets;
}
Closet struct_init_1 = Closet(); // or Closet struct_init_1 = {};
Closet struct_init_2 = {15, 3};
var struct_init_3 = Closet() { // Type inference also works
shirts = 15;
jackets = 3;
}
enum HouseSize { // An example of an enum
SMALL,
MODERATE,
BIG
}
/* Classes and Object-Oriented Programming */
class Message : GLib.Object { // Class Message extends GLib's Object
private string sender; // a private field
public string text {get; set;} // a public property
protected bool is_digital = true; // protected (this class and subclasses)
internal bool sent = false; // internal (classes in same package)
public void send(string message_sender) { // public method
sender = message_sender;
sent = true;
}
public Message() { // Constructor
// ...
}
}
interface InterfaceDemo { // Can be used as a mixin
// ...
}
// Since method overloading isn't possible, you can use named constructors
// to get the same functionality.
public class Calculator : GLib.Object {
public Calculator() {
}
public Calculator.with_name(string name) {
}
public Calculator.model(string model_id, string name = "") {
this.with_name(@"$model_id $name"); // Chained constructors with "this"
}
~Calculator() { } // Only needed if you're using manual memory management
}
var calc1 = new Calculator.with_name("Temp");
var calc2 = new Calculator.model("TI-84");
// Signals (a.k.a. events or event listeners) are a way to execute multiple
// methods with the same signature at the same time.
public class SignalDemo : GLib.Object {
public signal void sig_demo(int sig_demo_int); // Must be public
public static int main(string[] args) {
// main method; program does not compile without it
var sig_demo_class = new SignalDemo(); // New instance of class
sig_demo_class.sig_demo.connect((ob, sig_int) => { // Lambda used as handler
stdout.printf("%d\n", sig_int); // "ob" is object on which it is emitted
});
sig_demo_class.sig_demo(27); // Signal is emitted
return 0;
}
}
// You may use the connect() method and attach as many handlers as you'd like.
// They'll all run when the signal is emitted.
```
* More Vala documentation can be found [here](https://valadoc.org/).
* Read about building GUIs with GTK+ and Vala [here](http://archive.is/7C7bw).