all: add builtin channel type chan elem_type (#6126)

vlib/sync/channel_array_mut_test.v

@@ -0,0 +1,36 @@
+import sync
+
+const (
+	num_iterations = 10000
+)
+
+struct St {
+mut:
+	n int
+}
+
+// this function gets an array of channels for `St` references
+fn do_rec_calc_send(chs []chan mut St) {
+	mut s := St{}
+	for {
+		if !(&sync.Channel(chs[0])).pop(&s) {
+			break
+		}
+		s.n++
+		(&sync.Channel(chs[1])).push(&s)
+	}
+}
+
+fn test_channel_array_mut() {
+	mut chs := [chan mut St{cap: 1}, chan mut St{}]
+	go do_rec_calc_send(chs)
+	mut t := St{
+		n: 100
+	}
+	for _ in 0 .. num_iterations {
+		(&sync.Channel(chs[0])).push(&t)
+		(&sync.Channel(chs[1])).pop(&t)
+	}
+	(&sync.Channel(chs[0])).close()
+	assert t.n == 100 + num_iterations
+}