[BMX] Custom For Loop Iterators

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Pixel_Outlaw	Created : 02 July 2025 Edited : 03 July 2025 [BMX] Custom For Loop Iterators
Here is an example of how to implement your own Iterator for BlitzMax NG for loops. I've never seen somebody do this so I present it here. The For loops are designed this way and left open to the user such that you can make your own kind of iterator. This is a very common technique in other languages too. Especially C++, Java, C#, Rust - Anything with loops and an iterator interface. Beyond simple generators like below, it also provides a mechanism to use For loops with any new type of collection you define (think things like Red/Black trees, R-Trees etc) SuperStrict 'old habit - sue me ' Example of how to construct a custom iterator for your For loops. ' First you need an iterator that implements IIterator<type> ' It needs to have Current, and MoveNext Override the base class' virtual methods ' The new Iterator must be given by an IIterable<type> class you override. ' It will provide an IITerator implementation to the for loop which "pumps" it each loop ' This kind of behavior is useful for various generators taking the behavior OUT ' of the for loop. I can give you these classes and now you can use it without ' knowing how it works. ' Further ideas: What about an x,y iterator that kills those nested for loops? ' Fibonacci iterator: produces Fibonacci numbers up to a fixed count Type FibonacciIterator Implements IIterator<Int> ' These don't /have/ to be private but mutation would break the calculation Private Field lastValue:Int = -1 Private Field nextValue:Int = 1 Private Field currentIteration:Int = 0 Private Field iterations:Int = 10 Method New(iterations:Int) Self.iterations = iterations End Method ' Return the current Fibonacci number ' we need this to be public to match the call to Current Public Method Current:Int() Override Return nextValue End Method ' Move to next Fibonacci number, return True if available Method MoveNext:Int() Override If currentIteration >= iterations Then Return False End If Local temp:Int = nextValue + lastValue lastValue = nextValue nextValue = temp currentIteration :+ 1 Return True End Method End Type ' Fibonacci iterable: returns a new iterator each time Type FibonacciIterable Implements IIterable<Int> Field iterations:Int Method New(iterations:Int = 10) Self.iterations = iterations End Method Method GetIterator:IIterator<Int>() Override Return New FibonacciIterator(iterations) End Method End Type ' Here we use the new FibonacciIteratable ' You don't even need to know the formula to use it. ' The advantage here is that the For loop is /extensible/ ' We can't get here using the "step" value as it's constant. ' I can provide generators and other niceties for common looping patterns. ' The idea here is modularity. No more copy pasting iteration behavior ' over and over and over again. We've described a non linear computation ' in an IIterable instead. ' Now, if you're constantly writing loops for x and y you might ' consider a new IIterable that steps through those such that you ' never write that copy/pasted loop again. This would return an ' Point object. and you'd take the x and y there. ' It could even be generalized into an <n> dimensional one. For Local fibNum:Int = EachIn New FibonacciIterable(15) Print "Calling next Fibonacci number!" + fibNum Next --v

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[BMX] Custom For Loop Iterators

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