Type madness

src/compare.ts

@@ -0,0 +1,56 @@
+type digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';
+
+export type StrToNumber<X extends string> = _IsNumberString<X> extends true ? _StrToNumber<X, []> : never;
+type _IsNumberString<X extends string> = X extends `${infer first}${infer rest}` ? first extends digit ? true : false : false;
+type _StrToNumber<X extends string, Count extends unknown[]> =
+ `${Count['length']}` extends X ? Count['length'] : _StrToNumber<X, [unknown, ...Count]>
+
+export type EqualTo<X extends number, Y extends number> = X extends Y ? Y extends X ? true : false : false;
+
+export type IsNegative<X extends number> = `${X}` extends `-${infer rest}` ? true : false;
+export type Abs<X extends number> = `${X}` extends `-${infer rest}` ? StrToNumber<rest> : X;
+
+export type GreaterThan<X extends number, Y extends number> = EqualTo<X, Y> extends true ? false :
+ IsNegative<X> extends true ?
+ IsNegative<Y> extends true ? GreaterThan<Abs<Y>, Abs<X>> : false :
+ IsNegative<Y> extends true ? true : _GreaterThan<X, Y, []>;
+
+type _GreaterThan<X extends number, Y extends number, Count extends unknown[]> =
+ Count['length'] extends Y ? true :
+ Count['length'] extends X ? false :
+ _GreaterThan<X, Y, [unknown, ...Count]>;
+
+export type LessThan<X extends number, Y extends number> = EqualTo<X, Y> extends true ? false : GreaterThan<X, Y> extends true ? false : true;
+
+// tests
+const zeroEqualsZero: EqualTo<0, 0> = true;
+const numberEqualsNumber: EqualTo<number, number> = true;
+const zeroDoesNotEqualOne: EqualTo<0, 1> = false;
+const oneDoesNotEqualZero: EqualTo<0, 1> = false;
+const numberDoesNotEqualZero: EqualTo<number, 0> = false;
+const zeroDoesNotEqualNumber: EqualTo<0, number> = false;
+
+const isNegativeIsFalseForZero: IsNegative<0> = false;
+const isNegativeIsFalseForOne: IsNegative<1> = false;
+const isNegativeIsTrueForNegativeOne: IsNegative<-1> = true;
+
+const strToNumberString0IsZero: StrToNumber<'0'> = 0;
+const strToNumberString1IsOne: StrToNumber<'1'> = 1;
+const strToNumberString123IsOneHundredTwentyThree: StrToNumber<'123'> = 123;
+let strToNumberForFooIsNever: StrToNumber<'foo'>;
+
+const absZeroIsZero: Abs<0> = 0;
+const absOneIsOne: Abs<1> = 1;
+const absNegativeOneIsOne: Abs<-1> = 1;
+
+const zeroNotGreaterThanZero: GreaterThan<0, 0> = false;
+const oneGreaterThanZero: GreaterThan<1, 0> = true;
+const zeroNotGreaterThanOne: GreaterThan<0, 1> = false;
+const negativeOneNotGreaterThanZero: GreaterThan<-1, 0> = false;
+const zeroGreaterThanNegativeOne: GreaterThan<0, -1> = true;
+const negativeOneGreaterThanNegativeTwo: GreaterThan<-1, -2> = true;
+
+const zeroNotLessThanZero: LessThan<0, 0> = false;
+const oneNotLessThanZero: LessThan<1, 0> = false;
+const zeroLessThanOne: LessThan<0, 1> = true;
+