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digitalmars.D - Genie language updated

I have shown here a little the Genie language in the past, it' a version of the
Vala language with a cleaned up syntax. In the last months they have added
several new things, some of them can be interesting for D too.

Beside few comments of mine, most of the following text is quoted from this


Logical operations use names instead of symbols, so writing && or || for
mistake where you need a & or | (or the opposite bug) is avoided:

a and b
a or b
not (b)
a is not b
a is b


Nullable Types, they think they are a good idea, while so far this idea has
shipwrecked in D:

By default, Genie will make sure that all reference point to actual objects.
This means that you can't arbitrarily assign null to a variable. If it is
allowable for a reference to be null you should declare the type with a ?
modifier. This allows you to assert which types may be null, and so hopefully
avoid related errors in your code. This modifier can be placed both on
parameter types and return types of functions:

/* allows null to be passed as param and allows null to be returned */
def fn_allow_nulls (string? param) : string?
        return param
/* attempting to pass null as param will lead to that function aborting.
Likewise it may not return a null value */     
def fn_no_null (string param) : string
        return param  

(Genie performs such checks at run time (they can be disabled), D has can
totally avoid this.)


It even has built-in weak references, using the word "weak":

class Test
    Object o

    def get_weak_ref () : weak Object
        o = new Object()
        return o

Genie objects also have Events (aka Signals) by default.


Ownership transfer:

'#' is used to transfer ownership.

As a suffix of a parameter (or property) type. it means that ownership of the
object is transferred. As an operator, it can be used to avoid copies of
non-reference counting classes. e.g. 

var s = "hello"

/* s will be null when owner is transferred */
t : string = #s

print t

This means that s will be set to null and t inherits the reference/ownership of


'ref' and 'out' modifiers:

A method in Genie is passed zero or more parameters. The default behaviour when
a method is called is as follows:

    * Any value type parameters are copied to a location local to the function
as it executes.
    * Any reference type parameters are not copied, instead just a reference to
them is passed to the function. 

This behaviour can be changed with the modifiers 'ref' and 'out'.

'out' from the caller side
    you may pass an uninitialized variable to the method and you may expect it
to be initialized after the method returns 
'out' from callee side
    the parameter is considered uninitialized and you have to initialize it 
'ref' from caller side
    the variable you're passing to the method has to be initialized and it may
be changed or not by the method 
'ref' from callee side
    the parameter is considered initialized and you may change it or not 


Properties: one way to define them:

class Foo : Object
    prop name : string
    prop readonly count : int
    [Description(nick="output property", blurb="This is the utput property of
the Foo class")]    
    prop output : string
            return "output"
            _name = value   


isa operator, similar to the semantically-overloaded dynamic cast in D, to see
if a object is of a given Object type:

    var o = new list of string
    if o isa Object
        print "a list of string is an object"
    if o isa list of Object
        print "a list of string is a list of Object"
    if o isa Gee.Iterable
        print "a list of string implements Iterable"


Oct 31 2009