Improvements to matrix.eventable

* Support debug-logging to stderr by defining the MATRIX_EVENTABLE_DEBUG_LOG
  environment variable.
* Support for unhooking handlers from events.
* Simplify the low-level interface: eventable.functions() now returns the
  created functions directly, cutting down on an intermediate table.
* A new eventable.object() allows adding :hook(), :unhook() and :fire()
  methods to any table. Firing events always sends the table itself as first
  event parameter when firing any event.

test/eventable.lua

@@ -1,4 +1,3 @@
-#! /usr/bin/env lua
 --
 -- eventable.lua
 -- Copyright (C) 2016 Adrian Perez <aperez@igalia.com>
@@ -9,20 +8,20 @@
 local eventable = require "matrix.eventable"
 
 do -- Simple event
-   local ev = assert(eventable())
+   local fire, hook = assert(eventable())
    local flag = false
-   ev.hook("foo", function () flag = true end)
-   ev.fire("foo")
+   hook("foo", function () flag = true end)
+   fire("foo")
    assert(flag)
 end
 
 do -- Stop at first handler that returns some value
-   local ev = assert(eventable())
+   local fire, hook = assert(eventable())
    local flag1, flag2, flag3 = false, false, false
-   ev.hook("foo", function () flag1 = true end)
-   ev.hook("foo", function () flag2 = true ; return 42 end)
-   ev.hook("foo", function () flag3 = true ; return 0 end)
-   assert(ev.fire("foo") == 42)
+   hook("foo", function () flag1 = true end)
+   hook("foo", function () flag2 = true ; return 42 end)
+   hook("foo", function () flag3 = true ; return 0 end)
+   assert(fire("foo") == 42)
    assert(flag1 == true)
    assert(flag2 == true)
    assert(flag3 == false)
@@ -30,23 +29,45 @@ end
 
 do -- Arguments to eventable() are passed to handlers
    local obj = { answer = 42 }
-   local ev = assert(eventable(obj))
-   ev.hook("foo", function (o)
+   local fire, hook = assert(eventable(obj))
+   hook("foo", function (o)
       assert(o == obj)
       assert(o.answer == 42)
       o.answer = 0  -- Mutate
    end)
-   ev.fire("foo")
+   fire("foo")
    assert(obj.answer == 0)
 end
 
 do -- Multiple arguments passed to eventable
-   local ev = assert(eventable(42, "bar", nil, { v=10 }))
-   ev.hook("foo", function (a, s, n, o)
+   local fire, hook = assert(eventable(42, "bar", nil, { v=10 }))
+   hook("foo", function (a, s, n, o)
       assert(a == 42)
       assert(s == "bar")
       assert(n == nil)
       assert(o.v == 10)
    end)
-   ev.fire("foo")
+   fire("foo")
+end
+
+do -- Unhooking should work
+   local flag1, flag2 = false, false
+   local h1 = function () flag1 = true end
+   local h2 = function () flag2 = true end
+
+   local fire, hook, unhook = assert(eventable())
+   hook("foo", h1)
+   hook("foo", h2)
+   fire("foo")
+   assert(flag1 == true)
+   assert(flag2 == true)
+
+   flag1, flag2 = false, false
+   unhook("foo", h2)
+   fire("foo")
+   assert(flag1 == true)
+   assert(flag2 == false)
+
+   flag1, flag2 = false, false
+   unhook("foo")
 end