Add ArrayElement type helper

src/util/support/types.ts

@@ -80,3 +80,6 @@ export type Integer = TypeTag<'@extollo/lib.Integer'> & number
 export function isInteger(num: number): num is Integer {
     return !isNaN(num) && parseInt(String(num), 10) === num
 }
+
+export type ArrayElement<ArrayType extends readonly unknown[]> =
+    ArrayType extends readonly (infer ElementType)[] ? ElementType : never;