From 1334a4b925de64f0913c507666b73e22235ba366 Mon Sep 17 00:00:00 2001 From: Jim Pryor Date: Sun, 21 Nov 2010 15:18:32 -0500 Subject: [PATCH] week9 tweak Signed-off-by: Jim Pryor --- week9.mdwn | 2 ++ 1 file changed, 2 insertions(+) diff --git a/week9.mdwn b/week9.mdwn index 00900ea2..9c886b0f 100644 --- a/week9.mdwn +++ b/week9.mdwn @@ -100,6 +100,8 @@ Scheme is similar. There are various sorts of reference cells available in Schem (set-box! ycell 3) (+ x (unbox ycell))) +(C has explicit-style mutable variables, too, which it calls *pointers*. But simple variables in C are already mutable, in the implicit style.) + When dealing with explicit-style mutation, there's a difference between the types and values of `ycell` and `!ycell` (or `(unbox ycell)`). The former has the type `int ref`: the variable `ycell` is assigned a reference cell that contains an `int`. The latter has the type `int`, and has whatever value is now stored in the relevant reference cell. In an implicit-style framework though, we only have the resources to refer to the contents of the relevant reference cell. `y` in fragment [G] or the C snippet above has the type `int`, and only ever evaluates to `int` values. -- 2.11.0