One more Extension example

[nerobotParticipant]

We can often see such methods:

Monkey

Method Render( canvas:Canvas ) if image canvas.DrawImage( image,x,y ) End

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Method Render( canvas:Canvas )    if image canvas.DrawImage( image,x,y ) End

We can hide null-checking into extension:

Monkey

Class Image Extension Method Draw( canvas:Canvas,x:Float,y:Float ) if Self canvas.DrawImage( Self,x,y ) End End

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Class Image Extension Method Draw( canvas:Canvas,x:Float,y:Float ) if Self canvas.DrawImage( Self,x,y ) End End

And use it like this:

Monkey

image.Draw( canvas,0,0 )

1	image.Draw( canvas,0,0 )

Now we ask image to draw itself into canvas.

Just a playing around.

[DiffrenzyKeymaster]

Why the “If Self” ?

[nerobotParticipant]

Self can be null inside of extension.

[Mark SiblyKeymaster]

Self can be null inside of extension.

I never really considered this, not sure if I like it or not!

[edit] Don’t think I do like it, esp now there’s ‘?.’ – please don’t depend on it in future.

[nerobotParticipant]

It’s a feature of extensions!

We can write “safe” methods with that. Not only checking for nulls:

Monkey

' extension for some our class, like Method GetSafelySessionId() If Not Self or session.disposed Return -1 Return session.id End

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' extension for some our class, like Method GetSafelySessionId()     If Not Self or session.disposed Return -1     Return session.id End

Below is an example app to see Self is Null inside of extension:

Monkey

Namespace myapp #Import "<std>" #Import "<mojo>" Using std.. Using mojo.. Class MyWindow Extends Window Method New( title:String="Simple mojo app",width:Int=640,height:Int=480,flags:WindowFlags=Null ) Super.New( title,width,height,flags ) End Method OnRender( canvas:Canvas ) Override App.RequestRender() canvas.DrawText( "Hello World!",Width/2,Height/2,.5,.5 ) _img.Draw( canvas,50,50 ) End Field _img:Image ' don't assign to test extension End Function Main() New AppInstance New MyWindow App.Run() End Class Image Extension Method Draw( canvas:Canvas,x:Float,y:Float ) If Self canvas.DrawImage( Self,x,y ) Else Print "image is null" Endif End End

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Namespace myapp   #Import "<std>" #Import "<mojo>"   Using std.. Using mojo..   Class MyWindow Extends Window   Method New( title:String="Simple mojo app",width:Int=640,height:Int=480,flags:WindowFlags=Null )   Super.New( title,width,height,flags ) End   Method OnRender( canvas:Canvas ) Override App.RequestRender() canvas.DrawText( "Hello World!",Width/2,Height/2,.5,.5 ) _img.Draw( canvas,50,50 ) End Field _img:Image ' don't assign to test extension End   Function Main()   New AppInstance New MyWindow App.Run() End   Class Image Extension Method Draw( canvas:Canvas,x:Float,y:Float ) If Self canvas.DrawImage( Self,x,y ) Else Print "image is null" Endif End End

[nerobotParticipant]

Since v1.1.08 we can get a similar result for some cases with ?.operator :

_img?.Draw( … ) but it’s overhead in this case.

[DiffrenzyKeymaster]

Ohh!, I see, but I’m not sure Monkey should behave like that.

Self in a Method should always return an object IMO.

[nerobotParticipant]

Yes it should. Self in extension not equal to self in usual class.

Extension methods converted into plain functions by mx2cc. I think we need to have explanation of it in docs if have no yet.

[Mark SiblyKeymaster]

But how does user ‘know’ they are using an extension and it’s safe to skip ‘?.’?

If there’s a possiblility an object could be Null, coder should always use ?. or check for null IMO, regardless of whether  member is an extension or not. Extensions should behave as much like ‘normal’ methods as possible.

Making a special case for extensions just complicates the language more. My current thinking anyway…

[abakoboParticipant]

Yes, extension should behave just the same as classes/struct and a framework end-user shouldn’t need to pay attention to that kind of things IMHO.

[scurtyParticipant]

Oh the complications of scope. xD
What about Self.Ptr? Dereference it to get the Object.

[nerobotParticipant]

But how does user ‘know’ they are using an extension and it’s safe to skip ‘?.’?

If there’s a possiblility an object could be Null, coder should always use ?. or check for null IMO, regardless of whether member is an extension or not. Extensions should, IMO , behave as much like ‘normal’ methods as possible.

I agree.

Main rule here: all code – including extensions – should be fully documented!

I don’t invite you to write all null-checks inside of extensions, I just shown the way we *could* to use it.

There is a String.IsNullOrEmpty() extension method in c# to eliminate null checking until it has  ?. operator that comes with c# v6.0.

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