From f1609baebefccf7c5c2a81f6ebbd6cc474b79ef7 Mon Sep 17 00:00:00 2001
From: Andreas Rumpf <rumpf_a@web.de>
Date: Thu, 4 Jan 2018 14:06:50 +0100
Subject: [PATCH] Updated Destructors (rest)

---
 Destructors.rest | 57 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/Destructors.rest b/Destructors.rest
index d9c9941..9c039bc 100644
--- a/Destructors.rest
+++ b/Destructors.rest
@@ -167,3 +167,60 @@ Rule         Pattern                         Transformed into
   # object construction counts as proc call:
   c.add T() # calls version B
 
+
+Interactions with the GC
+========================
+
+The implementation of ``ref`` is likely to stay as it is today, a GC'ed pointer. But if the ``seq`` is not 
+baked by the GC how can ``ref seq[ref T]`` continue to work? The answer is yet another type bound operator
+called ``=trace``. With ``=trace`` a container can tell the GC how to access its contents for a GC's 
+sweeping/tracing step:
+
+.. code-block:: nim
+
+  proc `=trace`[T](s: seq[T]; a: Allocator) =
+    for i in 0 ..< s.len: `=trace`(s.data[i], a)
+
+``=trace`` always takes a second parameter, an ``allocator``. The new ``seq`` and ``string`` implementations
+are also based on allocators.
+
+
+Allocators
+==========
+
+The current design for an allocator looks like this:
+
+.. code-block:: nim
+
+  type
+    Allocator* {.inheritable.} = ptr object
+      alloc*: proc (a: Allocator; size: int; alignment = 8): pointer {.nimcall.}
+      dealloc*: proc (a: Allocator; p: pointer; size: int) {.nimcall.}
+      realloc*: proc (a: Allocator; p: pointer; oldSize, newSize: int): pointer {.nimcall.}
+
+  var
+    currentAllocator {.threadvar.}: Allocator
+
+  proc getCurrentAllocator*(): Allocator =
+    result = currentAllocator
+
+  proc setCurrentAllocator*(a: Allocator) =
+    currentAllocator = a
+
+  proc alloc*(size: int): pointer =
+    let a = getCurrentAllocator()
+    result = a.alloc(a, size)
+
+  proc dealloc*(p: pointer; size: int) =
+    let a = getCurrentAllocator()
+    a.dealloc(a, size)
+
+  proc realloc*(p: pointer; oldSize, newSize: int): pointer =
+    let a = getCurrentAllocator()
+    result = a.realloc(a, oldSize, newSize)
+
+
+Pluggable GC
+============
+
+To be written.