better C++ support wrt 'this'

tests/iter/tscheduler.nim

@@ -0,0 +1,76 @@
+discard """
+  output: '''a1 5
+a2 10
+a1 3
+a1 1
+a2 8
+a2 6
+a2 4
+a2 2'''
+"""
+
+import os, strutils, times, algorithm
+
+
+type TaskFn = iterator (): float
+
+type Task = object
+    coro: TaskFn
+    next_run: float
+
+
+type Scheduler = object
+    tasks: seq[Task]
+
+
+proc newScheduler(): Scheduler =
+    var s = Scheduler()
+    s.tasks = @[]
+    return s
+
+
+proc start(this: var Scheduler, task: TaskFn) =
+    var t = Task()
+    t.coro = task
+    t.next_run = 0.0
+    this.tasks.add(t)
+
+
+proc run(this: var Scheduler) =
+    while this.tasks.len > 0:
+        var dead: seq[int] = @[]
+        for i in this.tasks.low..this.tasks.high:
+            var task = this.tasks[i]
+            if finished(task.coro):
+                dead.add(i)
+                continue
+            if task.next_run <= epochTime():
+                task.next_run = task.coro() + epochTime()
+            this.tasks[i] = task
+        for i in dead:
+            this.tasks.delete(i)
+        if this.tasks.len > 0:
+            sort(this.tasks, proc (t1: Task, t2: Task): int = cmp(t1.next_run, t2.next_run))
+            sleep(int((this.tasks[0].next_run - epochTime()) * 1000))
+
+
+iterator a1(): float {.closure.} =
+    var k = 5
+    while k > 0:
+        echo "a1 $1" % [$k]
+        dec k, 2
+        yield 0.5
+
+
+iterator a2(): float {.closure.} =
+    var k = 10
+    while k > 0:
+        echo "a2 $1" % [$k]
+        dec k, 2
+        yield 1.5
+
+
+var sched = newScheduler()
+sched.start(a1)
+sched.start(a2)
+sched.run()