array: add filter() method

.gitignore

@@ -29,3 +29,4 @@ vjs
 # Thumbnails
 ._*
 .vrepl_temp.v
+a.out

vlib/builtin/array.v

@@ -329,3 +329,28 @@ pub fn (a []char) index(v char) int {
 	}
 	return -1
 }
+
+////////////// FILTER //////////////
+
+// Creates a new array with all elements that pass the test implemented by the provided function.
+pub fn (a  []string) filter(predicate fn(p_val string, p_i int, p_arr []string) bool) []string
+{
+	mut res := []string
+	for i := 0; i < a.len; i++  {
+		if predicate(a[i], i, a) {
+			res << a[i]
+		}
+	}
+	return res
+}
+
+pub fn (a []int) filter(predicate fn(p_val int, p_i int, p_arr []int) bool) []int
+{
+	mut res := []int
+	for i := 0; i < a.len; i++  {
+		if predicate(a[i], i, a) {
+			res << a[i]
+		}
+	}
+	return res
+}

vlib/builtin/array_test.v

@@ -296,3 +296,23 @@ fn test_in() {
 	assert !(4 in a)
 	assert !(0 in a)
 } 
+
+fn callback_1(val int, index int, arr []int) bool {
+	return val >= 2
+}
+
+fn callback_2(val string, index int, arr []string) bool {
+	return val.len >= 2
+}
+
+fn test_filter() {
+	a := [1, 2, 3, 4, 5, 6]
+	b := a.filter(callback_1)
+	assert b[0] == 2
+	assert b[1] == 3
+
+	c := ['v', 'is', 'awesome']
+	d := c.filter(callback_2)
+	assert d[0] == 'is'
+	assert d[1] == 'awesome'
+}