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Vala Collections: libgee

You should install the Vala collection library, libgee, from your distribution. More information about libgee is available from https://wiki.gnome.org/Projects/Libgee

Gee API Documentation

List Example

using Gee;

void main () {
    var list = new ArrayList<int> ();
    list.add (1);
    list.add (2);
    list.add (5);
    list.add (4);
    list.insert (2, 3);
    list.remove_at (3);
    foreach (int i in list) {
        stdout.printf ("%d\n", i);
    }
    list[2] = 10;                       // same as list.set (2, 10)
    stdout.printf ("%d\n", list[2]);    // same as list.get (2)
}

Compile and Run

$ valac --pkg gee-0.8 gee-list.vala
$ ./gee-list

You can use any type fitting into the size of a pointer (e.g. int, bool, reference types) directly as generic type argument: <bool>, <int>, <string>, <MyObject>. Other types must be "boxed" by appending a question mark: <float?>, <double?>, <MyStruct?>. The compiler will tell you this if necessary.

Set Example

Sets are unordered and do not contain duplicate elements.

using Gee;

void main () {
    var my_set = new HashSet<string> ();
    my_set.add ("one");
    my_set.add ("two");
    my_set.add ("three");
    my_set.add ("two");         // will not be added because it's a duplicate
    foreach (string s in my_set) {
        stdout.printf ("%s\n", s);
    }
}

Compile and Run

$ valac --pkg gee-0.8 gee-set.vala
$ ./gee-set

Map Example

Maps work like a dictionary. They store key - value pairs.

using Gee;

void main () {

    var map = new HashMap<string, int> ();

    // Setting values
    map.set ("one", 1);
    map.set ("two", 2);
    map.set ("three", 3);
    map["four"] = 4;            // same as map.set ("four", 4)
    map["five"] = 5;

    // Getting values
    int a = map.get ("four");
    int b = map["four"];        // same as map.get ("four")
    assert (a == b);

    // Iteration

    stdout.printf ("Iterating over entries\n");
    foreach (var entry in map.entries) {
        stdout.printf ("%s => %d\n", entry.key, entry.value);
    }

    stdout.printf ("Iterating over keys only\n");
    foreach (string key in map.keys) {
        stdout.printf ("%s\n", key);
    }

    stdout.printf ("Iterating over values only\n");
    foreach (int value in map.values) {
        stdout.printf ("%d\n", value);
    }

    stdout.printf ("Iterating via 'for' statement\n");
    var it = map.map_iterator ();
    for (var has_next = it.next (); has_next; has_next = it.next ()) {
        stdout.printf ("%d\n", it.get_value ());
    }
}

Compile and Run

$ valac --pkg gee-0.8 gee-map.vala
$ ./gee-map

Syntactic Sugar

There's syntactic sugar for testing if a collection contains an element:

if ("three" in my_set) {    // same as my_set.contains ("three")
    stdout.printf ("heureka\n");
}

Customizing the equality function

bool same_book (Book a, Book b) {
    return a.isbn == b.isbn;
}
    
// ...
        
var books = new Gee.ArrayList<Book> ((EqualFunc) same_book);

Implementing your own Iterable

You will have to implement two interfaces: Iterable with an iterator () method and an element_type property as well as an Iterator.

using Gee;

class RangeIterator : Object, Iterator<int> {

    private Range range;
    private int current;

    public RangeIterator (Range range) {
        this.range = range;
        this.current = range.from - 1;
    }

    public bool next () {
        if (!has_next ()) {
            return false;
        }
        this.current++;
        return true;
    }

    public bool has_next () {
        return this.current < this.range.to;
    }

    public bool first () {
        this.current = range.from;
        return true;
    }

    /* Here the 'new' keyword is used because Object already
       has a 'get' method. This will hide the original method.
       Otherwise you'll get a warning. */
    public new int get () {
        return this.current;
    }

    public void remove () {
        assert_not_reached ();
    }
}

public class Range : Object, Iterable<int> {

    public int from { get; private set; }
    public int to { get; private set; }

    public Range (int from, int to) {
        assert (from < to);
        this.from = from;
        this.to = to;
    }

    public Type element_type {
        get { return typeof (int); }
    }

    public Iterator<int> iterator () {
        return new RangeIterator (this);
    }
}

void main () {
    foreach (int i in new Range (10, 20)) {
        stdout.printf ("%d\n", i);
    }
}

Compile and Run

$ valac --pkg gee-0.8 iterable.vala
$ ./iterable

You could even add an each () method for Ruby or Groovy style iteration.

public class Range : Object, Iterable<int> {

    // ... (as above)

    public delegate void RangeEachFunc (int i);

    public void each (RangeEachFunc each_func) {
        foreach (int i in this) {
            each_func (i);
        }
    }
}

void main () {
    // Pass an anonymous function as parameter
    new Range (10, 20).each ((i) => {
        stdout.printf ("%d\n", i);
    });
}


Vala/Examples

Projects/Vala/GeeSamples (last edited 2016-08-09 15:55:57 by AlThomas)