### Example Struct Usage

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/structs.rst

A placeholder for demonstrating struct functionality. This snippet is intended to be expanded with concrete examples.

```vala
// ...

```

--------------------------------

### Download and Compile Vala Release Tarball

Source: https://github.com/gnome/vala/blob/main/README.md

Use this command to download a Vala release tarball, extract it, configure the build with a specified installation prefix, and then compile and install it. This method is useful for bootstrapping or when a pre-existing valac is not available.

```sh
curl --silent --show-error --location https://download.gnome.org/sources/vala/0.48/vala-0.48.25.tar.xz --output vala-bootstrap.tar.xz
tar --extract --file vala-bootstrap.tar.xz
cd vala-bootstrap
./configure --prefix=/opt/vala-bootstrap
make && sudo make install
```

--------------------------------

### Clean and Compile Vala from Repository

Source: https://github.com/gnome/vala/blob/main/README.md

Clean all untracked files from the Vala source tree using `git clean -dfx`, then run the autogen script, and compile and install. This is useful for starting a fresh build.

```sh
git clean -dfx
./autogen.sh
make && sudo make install
```

--------------------------------

### Vala Interface Virtual Method Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/interfaces.rst

Demonstrates an interface with a virtual default method and classes that either inherit or override this method. Shows how object instances use the most specific implementation.

```vala
/*
      This example gives you a simple interface, Yelper, with
      - one virtual default method, yelp

      It shows you two classes to demonstrate how these and overriding them behaves:
      - Cat, implementing Yelper (inheriting yelp)
      - Fox, implementing Yelper (overriding yelp)

      Important notes:
      - generally an object uses the most specific class's implementation
      - Yelper provides a default yelp (), but Fox overrides it
        - Fox overriding yelp () means that even casting Fox to Yelper still gives
          you Fox.yelp ()
      - as with the Speaker/speak () example, if a subclass wants to override an
        implementation (e.g. Fox.yelp ()) of a virtual interface method
        (e.g. Yelper.yelp ()), it must use 'new'
      - 'override' is used when overriding regular class virtual methods,
        but not when implementing interface virtual methods.
   */

   interface Yelper : Object {
     /* yelp: virtual, if we want to be able to override it */
     public virtual void yelp () {
       stdout.printf ("  Yelper yelps Yelp!\n");
     }
   }

   /* Cat: implements Yelper, inherits virtual yelp () */
   class Cat : Object, Yelper {
   }

   /* Fox: implements Yelper, overrides virtual yelp () */
   class Fox : Object, Yelper {
     public void yelp () {
       stdout.printf ("  Fox yelps Ring-ding-ding-ding-dingeringeding!\n");
     }
   }

   void main () {
     Yelper f = new Fox ();
     Yelper c = new Cat ();

     stdout.printf ("// Cat implements Yelper, inherits yelp\n");
     stdout.printf ("Cat as Yelper:\n");
     (c as Yelper).yelp ();  /* Yelper.yelp () */
     stdout.printf ("\nCat as Cat:\n");
     (c as Cat).yelp ();     /* Yelper.yelp () */

     stdout.printf ("\n\n// Fox implements Yelper, overrides yelp ()\n");
     stdout.printf ("Fox as Yelper:\n");
     (f as Yelper).yelp ();  /* Fox.yelp () */
     stdout.printf ("\nFox as Fox:\n");
     (f as Fox).yelp ();     /* Fox.yelp () */
   }
```

--------------------------------

### Interface Implementation Example in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/interfaces.rst

Demonstrates defining an interface with an abstract method and implementing it across multiple classes with varying inheritance and method overriding strategies. Shows how casting affects method resolution.

```vala
/*
      This example gives you a simple interface, Speaker, with
      - one abstract method, speak

      It shows you three classes to demonstrate how these and overriding them behaves:
      - Fox, implementing Speaker
      - ArcticFox, extending Fox AND implementing Speaker
        (ArcticFox.speak () replaces superclasses' .speak ())
      - RedFox, extending Fox BUT NOT implementing speaker
        (RedFox.speak () does not replace superclasses' .speak ())

      Important notes:
      - generally an object uses the most specific class's implementation
      - ArcticFox extends Fox (which implements Speaker) and implements Speaker itself,
        - ArcticFox defines speak () with new, so even casting to Fox or Speaker still
          gives you ArcticFox.speak ()
      - RedFox extends from Fox, but DOES NOT implement Speaker
        - RedFox speak () gives you RedFox.speak ()
        - casting RedFox to Speaker or Fox gives you Fox.speak ()
   */

   /* Speaker: extends from GObject */
   interface Speaker : Object {
     /* speak: abstract without a body */
     public abstract void speak ();
   }

   /* Fox: implements Speaker, implements speak () */
   class Fox : Object, Speaker {
     public void speak () {
       stdout.printf ("  Fox says Ow-wow-wow-wow\n");
     }
   }

   /* ArcticFox: extends Fox; must also implement Speaker to re-define
    *            inherited methods and use them as Speaker */
   class ArcticFox : Fox, Speaker {
     /* speak: uses 'new' to replace speak () from Fox */
     public new void speak () {
       stdout.printf ("  ArcticFox says Hatee-hatee-hatee-ho!\n");
     }
   }

   /* RedFox: extends Fox, does not implement Speaker */
   class RedFox : Fox {
     public new void speak () {
       stdout.printf ("  RedFox says Wa-pa-pa-pa-pa-pa-pow!\n");
     }
   }

   void main () {
     Speaker f = new Fox ();
     Speaker a = new ArcticFox ();
     Speaker r = new RedFox ();

     stdout.printf ("\n\n// Fox implements Speaker, speak ()\n");
     stdout.printf ("Fox as Speaker:\n");
     (f as Speaker).speak ();   /* Fox.speak () */
     stdout.printf ("\nFox as Fox:\n");
     (f as Fox).speak ();       /* Fox.speak () */

     stdout.printf ("\n\n// ArcticFox extends Fox, re-implements Speaker and " +
                    "replaces speak ()\n");
     stdout.printf ("ArcticFox as Speaker:\n");
     (a as Speaker).speak ();   /* ArcticFox.speak () */
     stdout.printf ("ArcticFox as Fox:\n");
     (a as Fox).speak ();       /* ArcticFox.speak () */
     stdout.printf ("\nArcticFox as ArcticFox:\n");
     (a as ArcticFox).speak (); /* ArcticFox.speak () */

     stdout.printf ("\n\n// RedFox extends Fox, DOES NOT re-implement Speaker but" +
                    " does replace speak () for itself\n");
     stdout.printf ("RedFox as Speaker:\n");
     (r as Speaker).speak ();   /* Fox.speak () */
     stdout.printf ("\nRedFox as Fox:\n");
     (r as Fox).speak ();       /* Fox.speak () */
     stdout.printf ("\nRedFox as RedFox:\ņ");
     (r as RedFox).speak ();    /* RedFox.speak () */
   }

```

--------------------------------

### Comment Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/gidl-metadata-format.rst

Comments in .metadata files start with a '#' and extend to the end of the line.

```gidl
# this is a comment
```

--------------------------------

### Compile Vala from Repository with Pre-installed valac

Source: https://github.com/gnome/vala/blob/main/README.md

Clone the Vala repository, run the autogen script, and then compile and install the compiler. This assumes a valac executable is already available in the system's PATH.

```sh
git clone https://gitlab.gnome.org/GNOME/vala
cd vala
./autogen.sh
make && sudo make install
```

--------------------------------

### Signal Declaration and Usage

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Shows how to declare a signal in a Vala class and the corresponding delegate type for handling the signal. This example sets up a basic signal emission mechanism.

```vala
public class Test : Object {
        public signal void test (int data);
}

delegate void TestHandler (Test t, int data);

void main () {
        Test t = new Test ();

```

--------------------------------

### Download and Compile from Vala Bootstrap Module

Source: https://github.com/gnome/vala/blob/main/README.md

Clone the Vala bootstrap module, touch stamp files, configure the build with a specified prefix, and then compile and install. This method is used when bootstrapping Vala without an existing valac.

```sh
git clone https://gitlab.gnome.org/Archive/vala-bootstrap
cd vala-bootstrap
touch */*.stamp
VALAC=/no-valac ./configure --prefix=/opt/vala-bootstrap
make && sudo make install
```

--------------------------------

### Conditional Compilation Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/preprocessor.rst

Demonstrates how to conditionally compile code using the PREPROCESSOR_DEBUG symbol, which can be defined via the '-D' compiler flag.

```vala
// Vala preprocessor example
public class Preprocessor : Object {

    /* public instance method */
    public void run () {
#if PREPROCESSOR_DEBUG
        // Use "-D PREPROCESSOR_DEBUG" to run this code path
        stdout.printf ("debug version");
#else
        // Normally, we run this code path
        stdout.printf ("production version");
#endif
    }
}

/* application entry point */
void main () {
    var sample = new Preprocessor ();
    sample.run ();
}
```

--------------------------------

### Vala Class Definition Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/overview.rst

An example of a simple class definition in Vala, demonstrating a field declaration. This code is illustrative and may not be usable out of context.

```vala
class MyClass : Object {
    int field = 1;
}
```

--------------------------------

### Compile Vala from Repository using Bootstrapped valac

Source: https://github.com/gnome/vala/blob/main/README.md

Clone the Vala repository, specify the path to a bootstrapped valac executable, run the autogen script, and then compile and install. This is used when compiling Vala with a previously bootstrapped version.

```sh
git clone https://gitlab.gnome.org/GNOME/vala
cd vala
VALAC=/opt/vala-bootstrap/bin/valac ./autogen.sh
make && sudo make install
```

--------------------------------

### Basic Metadata Line Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/gidl-metadata-format.rst

A non-comment line consists of a specifier followed by space-separated key-value parameters.

```gidl
foo.bar parameter1="value" parameter2="value"
```

--------------------------------

### Declaring Error Domains and Throwing/Catching Errors in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/errors.rst

Demonstrates the declaration of error domains, throwing new errors with messages, and catching specific errors within try-catch-finally blocks. This example illustrates the fundamental error handling flow in Vala.

```vala
errordomain ErrorType1 {
    CODE_1A
}

errordomain ErrorType2 {
    CODE_2A
}

void thrower () throws ErrorType1, ErrorType2 {
    throw new ErrorType2.CODE_1A ("Error");
}

void catcher () throws ErrorType2 {
    try {
        thrower ();
    } catch (ErrorType1 ex) {
        // Deal with ErrorType1
    } finally {
        // Tidy up
    }
}

void main () {
    try {
        catcher ();
    } catch (ErrorType2 ex) {
        // Deal with ErrorType2
    }
}
```

--------------------------------

### Hiding Symbols Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/gidl-metadata-format.rst

Demonstrates how to use specifiers to hide different types of symbols like Types, Functions, and Fields.

```gidl
Foo hidden="1"
```

```gidl
some_function hidden="1"
```

```gidl
Foo.bar hidden="1"
```

--------------------------------

### Wildcard Specifier Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/gidl-metadata-format.rst

Specifiers can use wildcards to apply metadata to multiple items. This example hides the 'klass' field in all types.

```gidl
*.klass hidden="1"
```

--------------------------------

### Vala Contract Programming Violation Example

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/methods.rst

Illustrates the output when a contract programming condition is violated in Vala. The example shows a CRITICAL message and the default return value when a postcondition fails.

```vala
void main () {
        stdout.printf ("%i\n", method_name (5, 3.0));
}
```

--------------------------------

### Continue Statement Syntax

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/statements.rst

The continue statement immediately transfers execution to the nearest enclosing while, do, for, or foreach statement, starting the next iteration.

```vala
continue;
```

--------------------------------

### Basic Enum Declaration Example in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/enumerated-types-enums.rst

This snippet demonstrates a basic enum declaration in Vala. It shows the syntax for defining an enum with named values.

```vala
// ...
```

--------------------------------

### Build Specific Vala Release Version

Source: https://github.com/gnome/vala/blob/main/README.md

Checkout a specific release tag (e.g., 0.56.17) from the Vala repository, clean untracked files, run the autogen script, and then compile and install. This allows building a particular version of Vala.

```sh
git checkout 0.56.17
git clean -dfx
./autogen.sh
make && sudo make install
```

--------------------------------

### Vala Generic Interface and Class Declaration and Usage

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/generics.rst

Demonstrates the declaration of a generic interface 'With<T>' and two classes, 'One' (non-generic, implementing With<int>) and 'Two<T,U>' (generic, implementing With<T>). Includes instantiation and usage examples in the main function.

```vala
public interface With<T> {
    public abstract void sett (T t);
    public abstract T gett ();
}

public class One : Object, With<int> {
    public int t;

    public void sett (int t) {
        this.t = t;
    }
    public int gett () {
        return t;
    }
}

public class Two<T,U> : Object, With<T> {
    public T t;

    public void sett (T t) {
        this.t = t;
    }
    public T gett () {
        return t;
    }

    public U u;
}

void main () {
    var o = new One ();
    o.sett (5);
    stdout.printf ("%d\n", o.t);

    var t = new Two<int,double?> ();
    t.sett (5);
    stdout.printf ("%d\n", t.t);

    t.u = 5.0f;
    stdout.printf ("%f\n", t.u);
}
```

--------------------------------

### Applying Attributes in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/attributes.rst

Attributes are applied using the [AnnotationName (details-list)] syntax before the declaration they modify. This example shows how to apply the CCode attribute with a specific C name for a variable.

```vala
[CCode (cname = "var_c_name")]
static int my_var;
```

--------------------------------

### Hello, World in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/overview.rst

The classic "Hello, world" program in Vala. Store this in a .vala file and compile using 'valac'.

```vala
int main (string[] args) {
    stdout.printf ("hello, world\n");
    return 0;
}
```

--------------------------------

### Declare Static and Instance Delegates

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/delegates.rst

Demonstrates the syntax for declaring static and instance delegates. Static delegates require the [CCode (has_target = false)] annotation.

```vala
[CCode (has_target = false)]
void DelegateName (int a, int b);
```

```vala
void DelegateName (int a, int b);
```

```vala
[CCode (has_target = false)]
void DelegateName () throws GLib.Error;
```

--------------------------------

### Class Instantiation in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/expressions.rst

Use the 'new' operator to create an instance of a class. Provide the class name and any required arguments for its creation method.

```vala
new type-name ( arguments )
```

--------------------------------

### Struct Creation Method Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/structs.rst

Illustrates the syntax for defining a struct's creation method, which controls instantiation. Unlike classes, any code can be placed within this method.

```vala
struct-creation-method-declaration:
   [ struct-access-modifier ] struct-name [ **.** creation-method-name ] **(** param-list **)** **{** statement-list **}**
```

--------------------------------

### Get Accessor Declaration in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Defines a custom getter for a property in Vala. This allows executing specific code when the property's value is retrieved.

```vala
[ class-member-visibility-modifier ] **get** **{** statement-list **}**
```

--------------------------------

### Using Statement Syntax

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/namespaces.rst

Illustrates the syntax for the 'using' statement, which allows Vala to search specified namespaces when an identifier cannot be resolved locally. This avoids the need for fully qualified names.

```vala
using namespace-list ;
```

--------------------------------

### Partial Class Definition

Source: https://github.com/gnome/vala/blob/main/doc/release-notes/vala-0.56.md

Shows how to define a class across multiple parts, potentially in different files, using the `partial` keyword. This is useful for managing very large or complex classes.

```vala
public partial class Foo : Object {
    public double bar { get; set; }
}

public partial class Foo : Initable {
    public virtual bool init (Cancellable? cancellable = null) {
        stdout.printf ("hello!\n");
        this.bar = 0.56;
        return true;
    }
}
```

--------------------------------

### Vala Class Creation Method Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Defines the syntax for declaring class creation methods, which can be used to instantiate classes with specific properties. The convention is to name these methods with 'with_' followed by a description of the properties being set.

```vala
[ class-member-visibility-modifier ] class-name [ **.** creation-method-name ] **(** param-list **)** **{** construction-assignments **}**
```

--------------------------------

### Basic Class Inheritance in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/concepts.rst

Demonstrates how a subclass can inherit from a superclass. A SubType instance is-a SuperType instance.

```vala
class SuperType {
    public int act () {
        return 1;
    }
}

class SubType : SuperType {
}
```

--------------------------------

### Instance Property Declaration in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Declares an instance property within a Vala class. Properties can have custom accessors (get, set, construct) and an optional default value. They can be virtual and overridden.

```vala
[ class-member-visibility-modifier ] [ class-method-type-modifier ] qualified-type-name property-name **{** accessors [ default-value ] **}** **;**
```

--------------------------------

### Vala Application Entry Point Definitions

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/overview.rst

Defines the acceptable signatures for the main entry point method in a Vala application. The method can be a non-instance method within a namespace or class, optionally accepting a string array for command-line arguments and returning an integer status code.

```vala
void main () { ... }
```

```vala
int main () { ... }
```

```vala
void main (string[] args) { ... }
```

```vala
int main (string[] args) { ... }
```

--------------------------------

### Vala Runtime Error with Fatal Log Levels

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/methods.rst

Demonstrates how setting fatal log levels in Vala can cause a runtime error when a contract programming assertion fails. This example shows the effect of `Log.set_always_fatal`.

```vala
Log.set_always_fatal (LogLevelFlags.LEVEL_CRITICAL | LogLevelFlags.LEVEL_WARNING);
stdout.printf ("%i\n", method_name (5, 3.0));
```

--------------------------------

### Connect and Disconnect Signals

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Demonstrates connecting a handler to a signal and then disconnecting it. Ensure the handler is correctly defined and passed.

```vala
TestHandler h = (t, data) => {
        stdout.printf ("Data: %d\n", data);
};

t.test (1);
t.test.connect (h);
t.test (2);
t.test.disconnect (h);
t.test (3);
```

--------------------------------

### Async Main Function with Yield

Source: https://github.com/gnome/vala/blob/main/doc/release-notes/vala-0.56.md

Demonstrates using an `async` main function to call asynchronous operations with `yield`. This is useful for I/O-bound tasks within the main program entry point.

```vala
async int main (string[] args) {
    string dir = args.length == 2 ? args[1] : ".";
    var file = File.new_for_commandline_arg (dir);
    try {
        FileEnumerator enumerator =
            yield file.enumerate_children_async (
                "standard::*,time:*",
                FileQueryInfoFlags.NOFOLLOW_SYMLINKS
            );
        List<FileInfo> children =
            yield enumerator.next_files_async (int.MAX);
        print ("total %lu\n", children.length ());
        foreach (var info in children) {
            // <file-type> <access-date> <size> <name>
            print ("%26s %24s %10"+int64.FORMAT+" B %s\n",
            info.get_content_type (),
            info.get_access_date_time ().to_string (),
            info.get_size (),
            info.get_name ());
        }
    } catch (Error e) {
        printerr ("failed to enumerate files - %s\n", e.message);
        return 1;
    }
    return 0;
}
```

--------------------------------

### Import GLib Namespace

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/namespaces.rst

Most Vala code depends on members of the GLib namespace. This snippet shows the standard way to import it.

```vala
using GLib;

```

--------------------------------

### Vala Contract Programming with Preconditions and Postconditions

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/methods.rst

Shows how to use 'requires' for preconditions and 'ensures' for postconditions in Vala methods to enforce contract programming principles. The 'result' variable represents the return value.

```vala
double method_name (int x, double d)
                requires (x > 0 && x < 10)
                requires (d >= 0.0 && d <= 1.0)
                ensures (result >= 0.0 && result <= 10.0) {
        return d * x;
}
```

--------------------------------

### Instance Delegate with Class Method

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/delegates.rst

Illustrates creating an instance delegate assigned to a class method. The 'this' keyword is implicitly available within the invoked method.

```vala
class Test : Object {
        private int data = 5;
        public void method (int a) {
                stdout.printf ("%d %d\n", a, this.data);
        }
}

delegate void DelegateType (int a);

void main () {
        var t = new Test ();
        DelegateType d = t.method;

        d (1);
}
```

--------------------------------

### Define a scope with local variables in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/concepts.rst

Illustrates a basic Vala method 'main' with local variable declarations and an arithmetic expression.

```vala
void main () {
    int a = 5;
    int b = a + 1;
}

```

--------------------------------

### Struct Instantiation in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/expressions.rst

Instantiate a struct by providing its name and optional arguments. An initializer block can be used to set field values.

```vala
type-name ( arguments ) { initializer }
```

--------------------------------

### Invoke Delegate and Pass as Parameter

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/delegates.rst

Shows how to invoke a delegate and pass it as a parameter to another method. The delegate is called using its variable name.

```vala
void f1 (int a) {
        stdout.printf ("%d\n", a);
}
...
void f2 (DelegateType d, int a) {
        d (a);
}
...
f2 (f1, 5);
```

--------------------------------

### Nested Namespace Declarations

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/namespaces.rst

Demonstrates two ways to declare nested namespaces: by nesting declarations or by using dot notation in a single declaration.

```vala
namespace NameSpaceName1 {
        namespace NameSpaceName2 {
        }
}

namespace NameSpaceName1.NameSpaceName2 {
}

```

--------------------------------

### Simple Class Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

The most basic way to declare a class in Vala.

```vala
class ClassName {
}

```

--------------------------------

### Virtual Properties in a Class Hierarchy

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Demonstrates the use of virtual properties in Vala, showing a base class with a virtual property and subclasses that either use the default implementation or override it.

```vala
namespace Properties {
    class Base : Object {
        protected int _number;
        public virtual int number {
            get {
                return this._number;
            }
            set {
                this._number = value;
            }
        }
    }

    /**
     * This class just use Base class default handle
     * of number property.
     */
    class Subclass : Base {
        public string name { get; set; }
    }

    /**
     * This class override how number is handle internally.
     */
    class ClassOverride : Base {
        public override int number {
            get {
                return this._number;
            }
            set {
                this._number = value * 3;
            }
        }
    }

    void main () {
        stdout.printf ("Implementing Virtual Properties...\n");
        var bc = new Base ();
        bc.number = 3;
        stdout.printf ("Class number = '" + bc.number.to_string () + "'\n");
        var sc = new Subclass ();
        sc.number = 3;
        stdout.printf ("Class number = '" + sc.number.to_string () + "'\n");
        var co = new ClassOverride ();
        co.number = 3;
        stdout.printf ("Class number = '" + co.number.to_string () + "'\n");
    }
}
```

--------------------------------

### Class Delegate Declaration Syntax

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Illustrates the syntax for defining a delegate within a class. Similar to namespace delegates, it supports class member visibility.

```vala
class-delegate-declaration:
   [ class-member-visibility-modifier ] return-type delegate delegate-name ( method-params-list );
```

--------------------------------

### Vala Class Instance Constructor Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Specifies the syntax for an instance constructor block. Code within this block is executed on every instance of the class after construction properties have been set.

```vala
**construct** **{** statement-list **}**
```

--------------------------------

### Abstract Properties in a Class Hierarchy

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Illustrates abstract properties in Vala, showcasing an abstract base class with an abstract property and a concrete subclass that implements it. The 'construct' keyword is used for initialization.

```vala
namespace Properties {
    abstract class Base : Object {
        public abstract string name { get; set construct; }

        construct {
            this.name = "NO_NAME";
        }
    }

    class Subclass : Base {
        private string _name;

        public override string name {
            get {
                return this._name;
            }
            set construct {
                this._name = value;
            }
        }

        /* This class have a default constructor that initializes
         * name as the construct block on Base, and a .with_name()
         * constructor where the user can set class derived name
         * property.
        */
        public Subclass.with_name (string name) {
            Object (name:name);
            this._name = name;
        }
    }

    void main () {
        stdout.printf ("Implementing Abstract Properties...\n");
        var sc = new Subclass.with_name ("TEST_CLASS");
        stdout.printf ("Class name = '" + sc.name + "'\n");
        var sc2 = new Subclass ();
        stdout.printf ("Class name = '" + sc2.name + "'\n");
    }
}
```

--------------------------------

### Delegate Invocation with Lambda Expression

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/delegates.rst

Demonstrates using a lambda expression to define the implementation for a delegate invocation, providing a concise inline method.

```vala
f2 (a => { stdout.printf ("%d\n", a); }, 5);
```

--------------------------------

### Array Instantiation in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/expressions.rst

Create an array of a specified type and size. Initializer expressions can be provided to populate the array upon creation.

```vala
new type-name [ sizes ] { initializer } { initializer }
```

--------------------------------

### Vala Class Class Constructor Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Defines the syntax for a class constructor block. This code executes once at the first use of the class and once at the first use of each subclass.

```vala
**class** **construct** **{** statement-list **}**
```

--------------------------------

### Vala Class Static Constructor Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Specifies the syntax for a static constructor block. This code runs exactly once in a program the first time a class or any of its subclasses are instantiated.

```vala
**static** **construct** **{** statement-list **}**
```

--------------------------------

### Vala Increment/Decrement Operations

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/expressions.rst

Demonstrates equivalent postfix and prefix increment/decrement operations in Vala. Use these for modifying variable values.

```vala
var postfix = i++;
var prefix = --j;
```

```vala
var postfix = i;
i += 1;

j -= 1;
var prefix = j;
```

--------------------------------

### Interface Instance Method Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/interfaces.rst

Syntax for declaring an instance method within a Vala interface. These methods can be abstract or have implementations.

```vala
[ class-member-visibility-modifier ] return-type method-name ( [ params-list ] ) method-contracts [ throws exception-list ] { statement-list }
```

--------------------------------

### Basic Namespace Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/namespaces.rst

Declares a simple namespace. Use this to create a distinct scope for your definitions.

```vala
namespace NameSpaceName {
}

```

--------------------------------

### Demonstrating Method Overriding and Polymorphism in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/concepts.rst

Illustrates how method overriding works with inheritance. The invoked method depends on the type the invoker believes it is dealing with.

```vala
SubType sub = new SubType ();
SuperType super = sub;

sub.act ();
super.act ();
```

--------------------------------

### Struct Method Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/structs.rst

Outlines the syntax for declaring methods within a struct. Methods can be static and may have specified return types, parameters, contracts, and exceptions.

```vala
struct-method-declaration:
   [ access-modifier ] [ struct-method-type-modifier ] return-type method-name **(** [ params-list ] **)** method-contracts [ **throws** exception-list ] **{** statement-list **}**
```

--------------------------------

### Dynamic Signal Invocation and Access

Source: https://github.com/gnome/vala/blob/main/doc/release-notes/vala-0.56.md

Demonstrates using the `dynamic` keyword to access object properties and invoke signals that might not be known at compile time. Signals can be emitted using `.emit()`.

```vala
dynamic Gst.Element appsink = Gst.ElementFactory.make ("appsink", "my_src");
appsink.max_buffers = 0;
appsink.eos.connect (on_eos);
Gst.Sample? res = appsink.pull_sample.emit ();
```

--------------------------------

### Vala Inline Method (Lambda) Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/methods.rst

Demonstrates how to declare an inline method using lambda syntax and assign it to a delegate type. This is a more succinct way to define methods that can be assigned to variables.

```vala
delegate int DelegateType (int a, string b);

int use_delegate (DelegateType d, int a, string b) {
        return d (a, b);
}

int make_delegate () {
        DelegateType d = (a, b) => {
                return a;
        };
        use_delegate (d, 5, "test");
}
```

--------------------------------

### Vala Class Instance Destructor Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Shows the syntax for declaring a class instance destructor. The documentation notes that the timing and behavior of destruction depend on the class type.

```vala
**~** class-name **(** **)** **{** statement-list **}**
```

--------------------------------

### Declare and initialize a string variable in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/concepts.rst

Declares a string variable 's' and initializes it with the value 'stringvalue'. The variable takes ownership of the new instance.

```vala
string s = "stringvalue";

```

--------------------------------

### Class Declaration Syntax

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Defines the general structure for declaring a class in Vala, including optional access modifiers, inheritance lists, and class members.

```vala
class ClassName : GLib.Object {

        public ClassName () {
        }

        public ClassName.with_some_quality (Property1Type property1value) {
                this.property1 = property1value;
        }
}
```

--------------------------------

### Interface Abstract Instance Method Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/interfaces.rst

Syntax for declaring an abstract instance method in a Vala interface. Implementing classes must provide a concrete implementation.

```vala
[ class-member-visibility-modifier ] abstract return-type method-name ( [ params-list ] ) method-contracts [ throws exception-list ] ;
```

--------------------------------

### Struct Field Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/structs.rst

Shows the syntax for declaring fields within a struct. Fields can be static and may be initialized with an expression.

```vala
struct-field-declaration:
   [ access-modifier ] [struct-field-type-modifier]
   qualified-type-name field-name [ **=** expression ] ;
```

--------------------------------

### Explicit Global Namespace Reference

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/namespaces.rst

Shows how to explicitly refer to an identifier in the global namespace using the 'global::' prefix. This is useful when a local variable shares a name with a global identifier.

```vala
global::identifier
```

--------------------------------

### Class Member Scope Resolution

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Demonstrates using 'this' to disambiguate between a local parameter and an instance field with the same name within a class method.

```vala
class ClassName {
        int field_name;
        void function_name (field_name) {
                this.field_name = field_name;
        }
}

```

--------------------------------

### Vala Preprocessor Syntax Overview

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/preprocessor.rst

Defines the general syntax for Vala preprocessor directives, including conditional compilation structures like #if, #elif, and #else, along with expression parsing.

```vala
[ any vala code ] [ pp-condition ] [ any vala code ]

pp-condition:
   #if pp-expression vala code [ pp-elif ] [ pp-else ] #endif

pp-elif:
   #elif pp-expression vala code [ pp-elif ]

pp-else:
   #else vala code

pp-expression:
   pp-or-expression

pp-or-expression:
   pp-and-expression [ || pp-and-expression ]

pp-and-expression:
   pp-binary-expression [ && pp-binary-expression ]

pp-binary-expression:
   pp-equality-expression
   pp-inequality-expression

pp-equality-expression:
   pp-unary-expression [ == pp-unary-expression ]

pp-inequality-expression:
   pp-unary-expression [ != pp-unary-expression ]

pp-unary-expression:
   pp-negation-expression
   pp-primary-expression

pp-negation-expression:
   ! pp-unary-expression

pp-primary-expression:
   pp-symbol
   ( pp-expression )
   true
   false

pp-symbol:
   identifier
```

--------------------------------

### Nested Functions for Code Structure

Source: https://github.com/gnome/vala/blob/main/doc/release-notes/vala-0.56.md

Illustrates nested functions, which are local to their containing function and can access its variables. This helps in structuring complex functions and reusing callbacks.

```vala
void write_streams (OutputStream stream1, OutputStream stream2, uint8[] data) {
    void nested_function (Object object_source, AsyncResult result) {
        OutputStream stream = object_source as OutputStream;
        try {
            ssize_t size = stream.write_async.finish (result);
            stdout.printf (@"Written $size bytes\n");
        } catch (Error e) {
            stderr.printf ("Error writing to stream: %s", e.message);
        }
    }
    
    stream1.write_async (data, nested_function);
    stream2.write_async (data, nested_function);
}
```

--------------------------------

### Return Statement Syntax

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/statements.rst

The return statement ends the execution of a method. If an expression is provided, its value becomes the return value of the method invocation.

```vala
return [ expression ];
```

--------------------------------

### Custom Array Length Type

Source: https://github.com/gnome/vala/blob/main/doc/release-notes/vala-0.56.md

Demonstrates how to specify a custom integer type (e.g., uint8) for the length of an array when declaring it.

```vala
string[] list = new string[10:uint8];
```

--------------------------------

### Basic Struct Declaration

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/structs.rst

Defines a simple struct with a single integer field. A struct must have at least one field unless specific conditions are met.

```vala
struct StructName {
        int some_field;
}
```

--------------------------------

### Throw Statement Syntax

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/statements.rst

The throw statement is used to raise an exception during program execution.

```vala
throw expression;
```

--------------------------------

### Abstract Instance Method Declaration in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/classes.rst

Declares an abstract instance method in a Vala class. Abstract methods have no implementation and must be overridden by concrete subclasses. They can only exist in abstract classes.

```vala
[ class-member-visibility-modifier ] **abstract** return-type method-name **(** [ params-list ] **)** method-contracts [ **throws** exception-list ] **;**
```

--------------------------------

### Basic Interface Declaration in Vala

Source: https://github.com/gnome/vala/blob/main/doc/manual/source/interfaces.rst

Defines the simplest possible interface structure in Vala. Interfaces are non-instantiable types.

```vala
interface InterfaceName {
}
```