Add unary end signature to integerRange function with implied start=0

Author: lionel-rowe

math/integer_range.ts

@@ -46,11 +46,45 @@ export type IntegerRangeOptions = {
  * assertEquals([...integerRange(5, 1, { step: -1 })], [5, 4, 3, 2]);
  * ```
  */
-export function* integerRange(
+export function integerRange(
   start: number,
   end: number,
   options?: IntegerRangeOptions,
+): Generator<number, undefined, undefined>;
+
+/**
+ * Creates a generator that yields integers in a range from 0 to `end`.
+ *
+ * Using the default options, yielded numbers are in the interval `[0, end)` with step size `1`.
+ *
+ * @param end The end of the range (exclusive by default)
+ * @param options Options for the range
+ * @returns A generator yielding integers in the specified range
+ *
+ * @example Usage
+ * ```ts
+ * import { integerRange } from "@std/math/integer-range";
+ * import { assertEquals } from "@std/assert";
+ * assertEquals([...integerRange(5)], [0, 1, 2, 3, 4]);
+ * ```
+ */
+export function integerRange(
+  end: number,
+  options?: IntegerRangeOptions,
+): Generator<number, undefined, undefined>;
+// deno-lint-ignore deno-style-guide/exported-function-args-maximum
+export function* integerRange(
+  startOrEnd: number,
+  endOrOptions?: number | IntegerRangeOptions,
+  maybeOptions?: IntegerRangeOptions,
 ): Generator<number, undefined, undefined> {
+  const hasStart = typeof endOrOptions === "number";
+  const [start, end, options] = [
+    hasStart ? startOrEnd : 0,
+    hasStart ? endOrOptions : startOrEnd,
+    hasStart ? maybeOptions : endOrOptions,
+  ];
+
   const { step = 1, includeStart = true, includeEnd = false } = options ?? {};
   if (step === 0) throw new RangeError("`step` must not be zero");
   for (const [k, v] of Object.entries({ start, end, step })) {
@@ -59,12 +93,18 @@ export function* integerRange(
     }
   }
 
+  if (start === end && !(includeStart && includeEnd)) return;
+
   const limitsSign = Math.sign(end - start);
   const stepSign = Math.sign(step);
   if (limitsSign !== 0 && limitsSign !== stepSign) return;
 
   if (includeStart) yield start;
-  if (start > end) { for (let i = start + step; i > end; i += step) yield i; }
-  else for (let i = start + step; i < end; i += step) yield i;
-  if (includeEnd && (start !== end || !includeStart)) yield end;
+
+  let i = 0;
+  const delta = Math.abs(step);
+  const maxDelta = Math.abs(end - start);
+  for (i += delta; i < maxDelta; i += delta) yield start + (i * stepSign);
+
+  if (includeEnd && (i * stepSign) + start === end) yield end;
 }

math/integer_range_test.ts

@@ -10,6 +10,11 @@ Deno.test("integerRange()", async (t) => {
     assertEquals([...range], []);
   });
 
+  await t.step("only include end (start defaulting to `0`)", () => {
+    const range = integerRange(5);
+    assertEquals([...range], [0, 1, 2, 3, 4]);
+  });
+
   await t.step("`step`", () => {
     assertEquals([...integerRange(1, 5, { step: 2 })], [1, 3]);
   });
@@ -34,13 +39,9 @@ Deno.test("integerRange()", async (t) => {
   });
 
   await t.step("`start` == `end`", () => {
-    assertEquals([...integerRange(0, 0)], [0]);
-    assertEquals([
-      ...integerRange(0, 0, { includeStart: true, includeEnd: true }),
-    ], [0]);
-    assertEquals([
-      ...integerRange(0, 0, { includeStart: false, includeEnd: true }),
-    ], [0]);
+    assertEquals([...integerRange(0, 0)], []);
+    assertEquals([...integerRange(0, 0, { includeEnd: true })], [0]);
+    assertEquals([...integerRange(0, 0, { includeStart: false })], []);
 
     // if _both_ are false, nothing is yielded
     assertEquals([
@@ -70,4 +71,17 @@ Deno.test("integerRange()", async (t) => {
       "`step` must not be zero",
     );
   });
+
+  await t.step("`includeEnd` with `step`", () => {
+    assertEquals([...integerRange(0, 2, { step: 2 })], [0]);
+    assertEquals([...integerRange(0, 2, { step: 2, includeEnd: true })], [
+      0,
+      2,
+    ]);
+    assertEquals([...integerRange(0, 3, { step: 2 })], [0, 2]);
+    assertEquals([...integerRange(0, 3, { step: 2, includeEnd: true })], [
+      0,
+      2,
+    ]);
+  });
 });