Unique Random Number Generation

using { /Verse.org/Random }
using { /Verse.org/Verse }

#Class of Util functions
UtilFunctions:= class():

    #Pool of all numbers that can be selected
    var NumPool : []int = array{}

    #Get a random int no repeated, Arg: MinNum: min int get, MaxNum: max int get
    GetRandomNumber(MinNum: int, MaxNum: int) :int =

        #Creat a numbers pools:
        if(NumPool.Length =0):
            Nums := for(Num:= MinNum..MaxNum):
                 Num
            set NumPool = Nums 

        #Get a random index of numbers in pool
        RandNum : int =  GetRandomInt(0,NumPool.Length-1);

        if(FinalNum := NumPool[RandNum]):
            #Remove the number corresponding to the index from the pool, and update the pool
            if (NewArray := NumPool.RemoveElement[RandNum]): 
                set NumPool = NewArray

            return FinalNum
        else:
            return 0

    #clear numbers appeared pool
    CleanNumPool():void = 
        #Clean the numbers appeared
        set NumPool = array{}