arrays: add more util functions and tests for them - find_first, find…

…_last, join_to_string (#18784)

vlib/arrays/arrays.v

@@ -1,5 +1,7 @@
 module arrays
 
+import strings
+
 // Common arrays functions:
 // - min / max - return the value of the minumum / maximum
 // - idx_min / idx_max - return the index of the first minumum / maximum
@@ -664,3 +666,53 @@ pub fn carray_to_varray[T](c_array_data voidptr, items int) []T {
 	unsafe { vmemcpy(v_array.data, c_array_data, total_size) }
 	return v_array
 }
+
+// find_first returns the first element that matches the given predicate
+// returns `none`, if there is no match found
+// Example: arrays.find_first([1, 2, 3, 4, 5], fn (arr int) bool { arr == 3}) // => 3
+pub fn find_first[T](array []T, predicate fn (elem T) bool) ?T {
+	if array.len == 0 {
+		return none
+	}
+	for item in array {
+		if predicate(item) {
+			return item
+		}
+	}
+	return none
+}
+
+// find_last returns the last element that matches the given predicate
+// returns `none`, if there is no match found
+// Example: arrays.find_last([1, 2, 3, 4, 5], fn (arr int) bool { arr == 3}) // => 3
+pub fn find_last[T](array []T, predicate fn (elem T) bool) ?T {
+	if array.len == 0 {
+		return none
+	}
+	for idx := array.len - 1; idx >= 0; idx-- {
+		item := array[idx]
+		if predicate(item) {
+			return item
+		}
+	}
+	return none
+}
+
+// join_to_string takes in a custom transform function and joins all elements into a string with
+// the specified separator
+[manualfree]
+pub fn join_to_string[T](array []T, separator string, transform fn (elem T) string) string {
+	mut sb := strings.new_builder(array.len * 2)
+	defer {
+		unsafe { sb.free() }
+	}
+	for i, item in array {
+		x := transform(item)
+		sb.write_string(x)
+		unsafe { x.free() }
+		if i < array.len - 1 {
+			sb.write_string(separator)
+		}
+	}
+	return sb.str()
+}

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'
+	}) == ''
+}