array: add index() method

vlib/builtin/array.v

@@ -290,3 +290,42 @@ fn compare_ints(a, b &int) int {
 pub fn (a mut []int) sort() {
 	a.sort_with_compare(compare_ints)
 }
+
+// Looking for an array index based on value. 
+// If there is, it will return the index and if not, it will return `-1`
+// TODO: Implement for all types
+pub fn (a []string) index(v string) int {
+	for i := 0; i < a.len; i++ {
+		if a[i] == v {
+			return i
+		}
+	}
+	return -1
+}
+
+pub fn (a []int) index(v int) int {
+	for i := 0; i < a.len; i++ {
+		if a[i] == v {
+			return i
+		}
+	}
+	return -1
+}
+
+pub fn (a []byte) index(v byte) int {
+	for i := 0; i < a.len; i++ {
+		if a[i] == v {
+			return i
+		}
+	}
+	return -1
+}
+
+pub fn (a []char) index(v char) int {
+	for i := 0; i < a.len; i++ {
+		if a[i] == v {
+			return i
+		}
+	}
+	return -1
+}

vlib/builtin/array_test.v

@@ -249,3 +249,29 @@ fn test_single_element() {
 	assert a[1] == 2
 	println(a)
 }	
+
+fn test_find_index() {
+	// string
+	a := ['v', 'is', 'great']
+	assert a.index('v') == 0
+	assert a.index('is') == 1
+	assert a.index('gre')  == -1
+
+	// int
+	b := [1, 2, 3, 4]
+	assert b.index(1) == 0
+	assert b.index(4) == 3
+	assert b.index(5) == -1
+
+	// byte
+	c := [0x22, 0x33, 0x55]
+	assert c.index(0x22) == 0
+	assert c.index(0x55) == 2
+	assert c.index(0x99) == -1
+
+	// char
+	d := [`a`, `b`, `c`]
+	assert d.index(`b`) == 1
+	assert d.index(`c`) == 2
+	assert d.index(`u`) == -1
+}