constructor

constructors

There is a subtle difference between
person{name:"Joe" address{street:"no way 123"}}
person:{name="Joe" address:{street="no way 123"}}

While both construct an object person, the variant with colon constructs pure data while the variant without colon constructs the person via a constructor, if available.

class person{
 init{
    id=random()
 }
}

a=person{} // preferred way
a=person() // works as constructor unless person is a function

By default classes are extendible, so person{name:"Joe" address{street:"no way 123"}} works as expected: the person object now has a name field and an id field via the init constructor.

There are situations where objects are meant to be immutable or non-extendible, or where successful construction depends on the right data at initialization time. These required fields can be denoted via exclamation mark:

class person{
  name!
  parent?
  address
}

Now every construction person{name:"blah"} must provide the name argument/field property.

The optional default for class fields is opposite to the function argument defaults, where un-required args can be marked with '?' or with default value. function log(n, base=10)=…

To avoid senseless redundant constructors, given fields need not be set by the constructors!! Only if special logic on the fields is desired, can they be set:

class person{
  init(name){
    this.name=name.upperCase
 }
}

In general, this special logic is to be avoided and it is often a sign of bad style.

Instead it should be moved to class functions, traits or even avoided altogether if there are generalized functions for those fields: print capitalized name of person