Possible to add method to Rect with "Extension" ?

[DiffrenzyKeymaster]

Is it possible to add a method to Rect, by the means of the Extention keyword/functionality?

If yes, please post an example, because my attemts results in compiler errors.

[Mark SiblyKeymaster]

Here you go..

Monkey

#Import "<std>" Using std.. Struct Rect<T> Extension Method Grow:Rect<T>( size:T ) Return New Rect<T>( min.x-size,min.y-size,max.x+size,max.y+size ) End End Function Main() Local r:=New Recti( 0,0,10,10 ) r=r.Grow( 5 ) Print r End

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#Import "<std>"   Using std..   Struct Rect<T> Extension   Method Grow:Rect<T>( size:T ) Return New Rect<T>( min.x-size,min.y-size,max.x+size,max.y+size ) End End   Function Main()   Local r:=New Recti( 0,0,10,10 ) r=r.Grow( 5 ) Print r End

Actually took me a few attempts to get right – you should be able to use plain ‘Rect’ inside the extension instead of ‘Rect<T>’ (the way you can inside normal class decls) but that’s not working. Will look into it eventually, but Rect<T> will always work.

[wiebowParticipant]

OK. Why would you want to use Extension instead of Extends?  Can someone explain the rationale behind it?

[Mark SiblyKeymaster]

OK. Why would you want to use Extension instead of Extends?

The main advantage of extensions is that they can be used with objects that you *didn’t* create. With inheritance, you need to be in control of the ‘new’ that creates the object.

So the above ‘Grow’ extension can be used with any Rect, not just ‘MyRects’ or some other class that Extends Rect. (also, you can’t currently extend structs anyway but that’s not really the point here!).

You can do all sorts of cool things with extensions, like add a DrawMysprite() method to canvas, To:String() or To:JsonValue() to *anything* etc.

There can also be multiple extensions of the same class, as opposed to single inheritance where you can create a new CoolRect1 or a CoolRect2 – but not both.

It’s important to note that extension methods are really just global functions (which is why I was a bit wary of adding them in the first place). But in mx2, some functionality can only be achieved via methods, eg: operators, To:String() etc, so they provide quite a nice way of dealing with that.

[DiffrenzyKeymaster]

Great, thanks for showing how

[seyhajinParticipant]

Hi,

I need to extend Vec2<T> struct with additionnal features but i have an errors with ‘Property’. Can you tell me if my code is correct and why he doesn’t work?

Monkey

#Import "<std>" Using std.. Struct Vec2<T> Extension '// By Property Property Angle:Float() Return ATan2(Self.Y, Self.X) Setter:Void(value:Float) Self.X = Cos(value) * Self.Length Self.Y = Sin(value) * Self.Length End Property Len:Double() 'Length extension Return Length Setter(value:Double) Local a:Double = ATan2(Self.Y, Self.X) Self.X = Cos(a) * value Self.Y = Sin(a) * value End '// By Method Method Angle2:Float() 'Test Return ATan2(Self.Y, Self.X) End Method Angle2:Vec2<T>(value:Float) 'Test Self.X = Cos(value) * Self.Length Self.Y = Sin(value) * Self.Length Return Self End Method Clone:Vec2<T>() Return New Vec2<T>(Self.X, Self.Y) End Method One:Vec2<T>() Self.X = 1.0 Self.Y = 1.0 Return Self End Method Zero:Vec2<T>() Self.X = 0.0 Self.Y = 0.0 Return Self End Method Limit:Vec2<T>(value:Double) Local i:T = value / ((Self.Length <> 0.0) ? Self.Length Else 1.0) i = (i < 1.0) ? i Else 1.0 Self.X = Self.X * i Self.Y = Self.Y * i Return Self End End Function Main() Local v:=New Vec2f(1,2) Print v.One() Print v.Zero() Print v.Angle2() Print v.Angle2(10.0) Print v.Angle '<--- Error : Property 'Angle' cannot be accessed from an instance of a different class v.Angle = 2.0 Print v Print v.Len '<--- Error : Property 'Len' cannot be accessed from an instance of a different class v.Len = 30.0 Print v End

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#Import "<std>"   Using std..   Struct Vec2<T> Extension '// By Property Property Angle:Float() Return ATan2(Self.Y, Self.X) Setter:Void(value:Float) Self.X = Cos(value) * Self.Length Self.Y = Sin(value) * Self.Length End Property Len:Double() 'Length extension Return Length Setter(value:Double) Local a:Double = ATan2(Self.Y, Self.X) Self.X = Cos(a) * value Self.Y = Sin(a) * value End '// By Method Method Angle2:Float() 'Test Return ATan2(Self.Y, Self.X) End Method Angle2:Vec2<T>(value:Float) 'Test Self.X = Cos(value) * Self.Length Self.Y = Sin(value) * Self.Length Return Self End Method Clone:Vec2<T>() Return New Vec2<T>(Self.X, Self.Y) End Method One:Vec2<T>() Self.X = 1.0 Self.Y = 1.0 Return Self End Method Zero:Vec2<T>() Self.X = 0.0 Self.Y = 0.0 Return Self End Method Limit:Vec2<T>(value:Double) Local i:T = value / ((Self.Length <> 0.0) ? Self.Length Else 1.0) i = (i < 1.0) ? i Else 1.0 Self.X = Self.X * i Self.Y = Self.Y * i Return Self End End   Function Main()         Local v:=New Vec2f(1,2)     Print v.One()     Print v.Zero()          Print v.Angle2()     Print v.Angle2(10.0)          Print v.Angle '<--- Error : Property 'Angle' cannot be accessed from an instance of a different class     v.Angle = 2.0     Print v          Print v.Len '<--- Error : Property 'Len' cannot be accessed from an instance of a different class     v.Len = 30.0     Print v End

[coconParticipant]

Doing some tests…

Monkey

#Import "<std>" Using std.. Struct Test Private Field value:Float End Struct Test Extension ' Mutator methods are allowed. Method SetValue(v:Float) value = v End ' Accessor methods are allowed. Method GetValue:Float() Return value End ' Properties are not allowed. 'Property GetSomething:String() ' Return "Hello" 'End End Function Main() Local a := New Test a.SetValue(100) Print(a.GetValue()) End

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#Import "<std>" Using std..   Struct Test Private Field value:Float End   Struct Test Extension ' Mutator methods are allowed. Method SetValue(v:Float) value = v End   ' Accessor methods are allowed. Method GetValue:Float() Return value End ' Properties are not allowed. 'Property GetSomething:String() ' Return "Hello" 'End End   Function Main() Local a := New Test a.SetValue(100) Print(a.GetValue()) End

[codifiesParticipant]

trouble using extern classes with any kind of extention

using either extends or extention I get Error : Super class ‘default.Rect’ has no default constructor
there is a slight complication in that the only a (float,float) constructor, but it will say the same if there is a () constructor…

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