let inline filter (f: ^T -> bool) (array: ( ^T)[]) = 
    
    if array = null then invalidArg "array" "Array can not be null."            
    if array.Length = 0 then invalidArg "array" "Array can not be empty."    
        
    let mutable count = 0

    for i = 0 to array.Length-1 do
        if f array.[i] then
            count <- count + 1
                    
    let result = Array.zeroCreate count
    let mutable j = 0
    for i = 0 to array.Length-1 do
        if f array.[i] then
            result.[j] <- array.[i]
            j <- j + 1
    result