Closures?

[skn3Participant]

Pretty excited to see that mx2 appears to support closures!

Is the following code valid/safe in mx2?

What are the consequences/penalties/performance-issues by doing this? For example, what is happening (internally) to name:String once CreateItem has returned?

Monkey

Function Main:Void() Local item1 := CreateItem("closure1") Local item2 := CreateItem("closure2") item1.Run() item2.Run() End Function CreateItem:Item(name:String) Local item := New Item item.Callback = Lambda() Print "closure:"+name'this is reading name from the closure above it End Return item End Class Item Field Callback:Void() Method Run:Void() Callback() End End

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Function Main:Void() Local item1 := CreateItem("closure1") Local item2 := CreateItem("closure2") item1.Run() item2.Run() End   Function CreateItem:Item(name:String) Local item := New Item item.Callback = Lambda() Print "closure:"+name'this is reading name from the closure above it End Return item End   Class Item Field Callback:Void() Method Run:Void() Callback() End End

[Mark SiblyKeymaster]

Yep, that’s fine. I use stuff like this all over the place in Ted2 , eg: mojox.Action.

name:String is ‘captured’ by the lamba, which effectively means it’s copied into a private area of the lamba. But since strings are immutable and reference counted, this is very cheap.

[skn3Participant]

That is good news! Might be worth adding an example to the Lambda docs. I was going to do it in the online Manual, but it looks like comments are only available for modules?

 

Here is how I am using it, very handy!

Monkey

Method LoadAtlas:Atlas(path:String) 'check if it exists already Local atlas := atlases[path] 'do we need to load it? If atlas = Null 'yup, load it atlas = Atlas.Load(path) If atlas 'add discarded event to atlas atlas.OnDiscarded += Lambda() atlases.Remove(path) End 'now cache it atlases[path] = atlas Endif Endif 'return it now 😉 Return atlas End

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Method LoadAtlas:Atlas(path:String) 'check if it exists already Local atlas := atlases[path] 'do we need to load it? If atlas = Null 'yup, load it atlas = Atlas.Load(path) If atlas 'add discarded event to atlas atlas.OnDiscarded += Lambda() atlases.Remove(path) End 'now cache it atlases[path] = atlas Endif Endif 'return it now Return atlas End

[papgarParticipant]

It would be nice to have more lambda examples in docs so we can see how this feature is useful for applications/games.

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