Constructor/Destructor

Constructor

The constructor syntax in THP is inspired by Kotlin.

Constructors are declared like function definitions:

//          |this is the constructor |
class Animal(String fullname, Int age)

// Creating an instance
val cat = Animal("Michi", 3)thp
    

A constructor declared that way is public.

Note that the parameters in the constructor (fullname, age above) are not properties, and cannot be used inside the class methods, only in the init block and properties declaration.

To declare properties in the constructor see Constructor promotion.

Constructor visibility

If you want to declare a constructor as protected or private you need to add the constructor keyword, after the visibility modifier:

// Cow has a protected constructor
class Cow
protected constructor(String color)

// Bat has a private constructor
class Bat
private constructor(Int height)thp
    

Init block

The init block allow us to run code during the construction of the instance:

class Dog(String name)
{
    pub String name = name
    Int name_len = name.length

    init
    {
        print("Dog created: {name}")
    }
}thp
    

Constructor promotion

Constructor parameters can serve as class properties. This is done by adding a modifier and var/val.

class Parrot(
    // A public property
    pub val String name,
    // A protected property
    protected var Int age,
    // A private property
    var String last_name,
)thp
    

By using this syntax you are declaring properties and assigning them at the same time.

The contructor parameters can also have default values.

Derived properties

You can declare properties whose values depend on values on the constructor.

class Animal(
    val String fullname,
)
{
    // A property whose value depends on `fullname`
    // This is executed after the contructor
    pub val Int name_length = fullname.length
}

val a2 = Animal("Doa")
print(a2.name_length)   //: 3thp
    

Constructor that may fail

TBD

Proposal 1:

class PrayingMantis(String name) -> self!Errorthp
    

Proposal 2:

class PrayingMantis(String name)
throws Errorthp
    

Proposal 3:

class PrayingMantis(String name)
{
    init -> self!Error
    {
        // Something that may fail
    }
}thp
    

Destructor

The destructor in THP is the same as PHP.

class Owl
{
    pub fun __destruct()
    {
        // Cleanup
        print("Destroying Owl...")
    }
}thp