Function GetFromList(list,index)
Monkey Forums/Monkey Programming/Function GetFromList(list,index)
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| Hi, I wan't to have a function that gets an object at index from a list. Monkey lists do not support list.Get() anymore (why?). The function shall work indenpendent from which kind of object is in there. Function GetFromList:Object(list:List<Object>, index:Int) Local count:int For Local o:Object = eachin list if count = index Return o EndIf count+=1 Next Return NULL End Function This one fails with "Wrong number of type arguments for class List<T>" |
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| Try using a Stack instead. |
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| All my old code from Blitzmax is with lists. I want to stay with lists. |
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| In Monkey every container such as lists have to have a specific type. First, this ensures you can't just put anything in there which is bad practice anyway (you can still use polymorphism) Also it avoids casting everytime you want an object of that container (bad for performance). If you want to have indexed access, a list is the wrong container anyway. A stack like Samah mentioned would be a better fit. Other alternatives are simple arrays or the ArrayList in diddy or extending a list with your own class. |
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| Hi Volker, here is a quick example. It creates a static helper class: [monkeycode] Import mojo Function Main : Int() '// User which ever < Class > you wish and pass it your list ListExtension< blah >.GetFromList( New List< blah >, 0 ) Return 1 End Function Class ListExtension< T > Function GetFromList : T( list : List< T >, index : Int ) Local count : int For Local this : T = Eachin list If count = index Then Return this count = count + 1 Next Return Null End Function End Class [/monkeycode] The other option as Gerry suggested below is to extend list: [monkeycode] Import mojo Function Main : Int() Local myList : ListExtension< Object > = New ListExtension< Object > Local firstIndex : Object = myList.GetFromList( 0 ) Return 1 End Function Class ListExtension< T > Extends List< T > method GetFromList : T( index : Int ) Local count : int For Local this : T = Eachin Self If count = index Then Return this count = count + 1 Next Return Null End method End Class [/monkeycode] |
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| You could add it to (or extend) monkey.list |
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| Thanks guys, will have to think about it. |
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| If you are indexing lists then you do not want to stay with lists, you want to use stacks. |
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| [monkeycode]Local foo:Stack<Bar> = New Stack<Bar> foo.Push(something) ' like List.AddLast foo.Pop(something) ' like List.RemoveLast foo.Get(index) foo.Set(index, value)[/monkeycode] Just use a stack instead. It's a built-in class. |
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| Stacks fail when removing objects in a eachin loop. No concurrency check. |
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| Diddy's ArrayList does a concurrency check and will throw an exception if you try to modify the list within an eachin loop. However, you can manually retrieve the Enumerator object and traverse back and forth, removing as you go by calling Remove() on the enumerator. |
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| Yeah I was indexing Lists too...I've just switched to stacks. |
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| Just another comment even though you are not using a list anymore. After some tests last year with blitmax I found it a very good middle ground between array and list access to avoid using the foreach enumerators. I would assume the same will occur in monkey and at least you wont be creating garbage enumerator objects. ( http://www.blitzbasic.com/Community/posts.php?topic=97352 ) So you could do your extended list method like so: Class ListExtension<T> Extends List<T> Method GetFromList:T(findIndex:Int) Local node:= FirstNode() Local nodeIndex:Int While node If nodeIndex = findIndex Return node.Value() nodeIndex += 1 node = node.NextNode() Wend Return Null End method End Class Some would argue it is pointless micro optimizations but well there is no harm in doing it this way and its not really that much more effort. |
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