arrays: add generic copy fn (#13677)

vlib/arrays/arrays.v

@@ -530,3 +530,15 @@ fn swap_nonoverlapping<T>(x_ &T, y_ &T, count int) {
 		memswap(x, y, len)
 	}
 }
+
+// copy copies the `src` array elements to the `dst` array.
+// The number of the elements copied is the minimum of the length of both arrays.
+// Returns the number of elements copied.
+pub fn copy<T>(dst []T, src []T) int {
+	min := if dst.len < src.len { dst.len } else { src.len }
+	if min > 0 {
+		blen := min * int(sizeof(T))
+		unsafe { vmemmove(&T(dst.data), src.data, blen) }
+	}
+	return min
+}

vlib/arrays/arrays_test.v

@@ -264,3 +264,20 @@ fn test_rotate_left_string() {
 	rotate_left(mut x, 2)
 	assert x == ['x3', 'x4', 'x5', 'x6', 'x1', 'x2']
 }
+
+fn test_copy() {
+	mut a := [1, 2, 3]
+	mut b := [4, 5, 6]
+	assert copy(b, a) == 3
+	assert b == [1, 2, 3]
+	// check independent copies
+	b[0] = 99
+	assert a[0] == 1
+	// check longer src
+	b << 7
+	assert copy(a, b) == 3
+	assert a == [99, 2, 3]
+	// check longer dst
+	assert copy(b, [8, 9]) == 2
+	assert b == [8, 9, 3, 7]
+}