arrays: add more util functions and tests for them - find_first, find_last, join_to_string (#18784)

vlib/arrays/arrays_test.v

@@ -404,3 +404,71 @@ fn test_map_of_counts() {
 	assert map_of_counts(['abc', 'def', 'abc']) == {'abc': 2, 'def': 1}
 	// vfmt on
 }
+
+struct FindTest {
+	name string
+	age  int
+}
+
+const test_structs = [FindTest{'one', 1}, FindTest{'two', 2},
+	FindTest{'three', 3}, FindTest{'one', 4}]
+
+fn test_find_first() {
+	// element in array
+	a := [1, 2, 3, 4, 5]
+	assert find_first[int](a, fn (arr int) bool {
+		return arr == 3
+	})? == 3, 'find element couldnt find the right element'
+
+	// find struct
+	find_by_name := find_first(arrays.test_structs, fn (arr FindTest) bool {
+		return arr.name == 'one'
+	})?
+	assert find_by_name == FindTest{'one', 1}
+
+	// not found
+	if _ := find_first(arrays.test_structs, fn (arr FindTest) bool {
+		return arr.name == 'nothing'
+	})
+	{
+		assert false
+	} else {
+		assert true
+	}
+}
+
+fn test_find_last() {
+	// // element in array
+	a := [1, 2, 3, 4, 5]
+	assert find_last[int](a, fn (arr int) bool {
+		return arr == 3
+	})? == 3, 'find element couldnt find the right element'
+
+	// find struct
+	find_by_name := find_last(arrays.test_structs, fn (arr FindTest) bool {
+		return arr.name == 'one'
+	})?
+	assert find_by_name == FindTest{'one', 4}
+
+	// not found
+	if _ := find_last(arrays.test_structs, fn (arr FindTest) bool {
+		return arr.name == 'nothing'
+	})
+	{
+		assert false
+	} else {
+		assert true
+	}
+}
+
+fn test_join_to_string() {
+	assert join_to_string[FindTest](arrays.test_structs, ':', fn (it FindTest) string {
+		return it.name
+	}) == 'one:two:three:one'
+	assert join_to_string[FindTest](arrays.test_structs, '', fn (it FindTest) string {
+		return it.name
+	}) == 'onetwothreeone'
+	assert join_to_string[int]([]int{}, ':', fn (it int) string {
+		return '1'
+	}) == ''
+}