From bb190ddbba216251f2a8490adf9feadf0dbb7104 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Mon, 25 Jan 2010 23:43:41 +0100
Subject: [PATCH] Add ASCII art representing the basic struct layout.

* libguile/struct.h: Add ASCII art version of the basic struct layout as
  shown in Andy's diagrams.
---
 libguile/struct.h | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/libguile/struct.h b/libguile/struct.h
index 012d9b6e7..374a5ce74 100644
--- a/libguile/struct.h
+++ b/libguile/struct.h
@@ -33,9 +33,37 @@
    in turn means we need support for changing the "class" (vtable) of an
    "instance" (struct). This necessitates some indirection and trickery.
 
-   I would like to write this all up here, but for now:
+   To summarize, structs are laid out this way:
+
+                  .-------.
+                  |       |
+     .----------------+---v------------- -
+     | vtable | data  | slot0 | slot1 |
+     `----------------+----------------- -
+         |        .-------.
+         |        |       |
+     .---v------------+---v------------- -
+     | vtable | data  | slot0 | slot1 |
+     `----------------+----------------- -
+         |
+         v
+
+        ...
+                  .-------.
+         |        |       |
+     .---v------------+---v------------- -
+   .-| vtable | data  | slot0 | slot1 |
+   | `----------------+----------------- -
+   |     ^
+   `-----'
+
+   The DATA indirection (which corresponds to `SCM_STRUCT_DATA ()') is necessary
+   to implement class redefinition.
+
+   For more details, see:
 
      http://wingolog.org/archives/2009/11/09/class-redefinition-in-guile
+
  */
 
 /* All vtables have the following fields. */