On 08/30/2010 11:04 PM, Nicolas Ojeda Bar wrote:
Hello,
I need extensible records, and the code below seems to
work. Are there any pitfall that I should be aware of?
Could this mess up the GC?
# type t0 = { a : int };
# type t1 = { a2 : int; b : int };
# value x1 = { a2 = 3; b = 5 };
# value x0 : t0 = Obj.magic x1;
value x0 = { a = 3 }
# value x0' : t1 = Obj.magic x0;
value x0' = { a2 = 3; b = 5 }
You should also be aware that structural equality (=) is untyped, so you
might get surprised by this:
type t0 = { a : int; };;
# type t1 = { a2 : int; b : int; }
type t1 = { a2 : int; b : int; };;
# let x = {a2=3; b=1};;
val x : t1 = {a2 = 3; b = 1}
# let y = {a2=3; b=2};;
val y : t1 = {a2 = 3; b = 2}
# let x0 : t0 = Obj.magic x;;
val x0 : t0 = {a = 3}
# let y0 : t0 = Obj.magic y;;
val y0 : t0 = {a = 3}
# x0 = y0;;
- : bool = false
x0 and y0 look structurally equal, but they're not!
The same oddity will show up with Pervasives.compare and
Pervasives.hash, just to mention those two.
Bruno.
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