initializer_blocks.md

dyvil	v0.32.0

Initializer Blocks

Initializer Blocks are a way to run code during the initialization of a class or an instance. You can declare one by using the init keyword in a class body:

class Foo
{
    var bar: int
    
    init
    {
        var i: int = someValue
        if (someCondition)
        {
            i *= 2
        }
        this.bar = i
        
        print "Initialized"
    }
}

new Foo // prints 'Initialized'

When creating an instance of the Foo class, the initializer block runs as if it was part of a constructor body. There is a major difference between initializer blocks and no-arg constructors, however. While the latter are separate and only one of them runs, initializers are shared. This means they run regardless of which constructor was called.

class Bar
{
    public new(i: int)
    {
        print "new(int)"
    }
    
    public new(s: String)
    {
        print "new(String)"
    }
    
    init
    {
        print "Initializer"
    }
}

new Bar(1)   // prints 'Initializer', 'new(int)'
new Bar("A") // prints 'Initializer', 'new(String)'

Static Initializer Blocks

Adding the static modifier makes a Static or Class initializer. They run at most once, when the enclosing class is loaded.

class Baz
{
    static init
    {
        print "Static Init"
    }
    
    init
    {
        print "Init"
    }
}

new Baz // prints 'Static Init', 'Init'
new Baz // prints 'Init'
new Baz // prints 'Init'