block9.ts

declare class RangeValueTag<Min extends number, Max extends number> {
    private __minValue: Min;
    private __maxValue: Max;
}

type InRangeNumber<Min extends number, Max extends number> = 
       number & RangeValueTag<Min, Max>;

function isInRangeNumber<Min extends number, Max extends number>(
   value: number, 
   min: Min, 
   max: Max
): value is InRangeNumber<Min, Max> {
return value > min && value < max;
}

const a = 100;
if (isInRangeNumber(a, 10, 1000)) {
   const b: InRangeNumber<10, 1000> = a; //compile
}