improve some array types to handle readonly arrays

.changeset/eighty-rice-mix.md

@@ -0,0 +1,5 @@
+---
+"@grogarden/util": patch
+---
+
+improve some array types to handle readonly arrays

src/lib/array.ts

@@ -1,6 +1,10 @@
+import type {Array_Element} from '$lib/types.js';
+
+// TODO try to cange to readonly again, see if upstream errors are tolerably fixed
 export const EMPTY_ARRAY: any[] = Object.freeze([]) as any;
 
-export const to_array = <T>(value: T | T[]): T[] => (Array.isArray(value) ? value : [value]);
+export const to_array = <T>(value: T): T extends readonly any[] ? T : T[] =>
+	Array.isArray(value) ? value : ([value] as any);
 
 export const remove_unordered = (array: any[], index: number): void => {
 	array[index] = array[array.length - 1];
@@ -11,7 +15,7 @@ export const remove_unordered = (array: any[], index: number): void => {
  * Returns a function that returns the next item in the `array`
  * in a linear sequence, looping back to index 0 when it reaches the end.
  */
-export const to_next = <T>(array: T[]): (() => T) => {
+export const to_next = <T extends readonly any[]>(array: T): (() => Array_Element<T>) => {
 	let i = -1;
 	return () => {
 		i++;

src/lib/random.test.ts

@@ -85,7 +85,7 @@ test__random_item('a and b', () => {
 	const items = ['a', 'b'];
 	const results = [];
 	for (let i = 0; i < 20; i++) {
-		const result = random_item(items)!;
+		const result = random_item(items);
 		assert.ok(items.includes(result));
 		results.push(result);
 	}
@@ -97,7 +97,7 @@ test__random_item('1 to 5', () => {
 	const items = [1, 2, 3, 4, 5];
 	const results = [];
 	for (let i = 0; i < 100; i++) {
-		const result = random_item(items)!;
+		const result = random_item(items);
 		assert.ok(items.includes(result));
 		results.push(result);
 	}

src/lib/random.ts

@@ -1,3 +1,5 @@
+import type {Array_Element} from '$lib/types.js';
+
 export const random_float = (min: number, max: number, random = Math.random): number =>
 	random() * (max - min) + min;
 
@@ -11,8 +13,10 @@ export const random_int = (min: number, max: number, random = Math.random): numb
 
 export const random_boolean = (random = Math.random): boolean => random() > 0.5;
 
-export const random_item = <T>(arr: T[], random = Math.random): T =>
-	arr[random_int(0, arr.length - 1, random)];
+export const random_item = <T extends readonly any[]>(
+	arr: T,
+	random = Math.random,
+): Array_Element<T> => arr[random_int(0, arr.length - 1, random)];
 
 /**
  * Mutates `array` with random ordering.