[Pharo-project] Pharo changing the game

Martin McClure martin at hand2mouse.com
Fri Feb 12 16:06:26 EST 2010

Stéphane Ducasse wrote:
>> However, since VW already implements immutability, it would probably
>> be beneficial to chose an API that is close to the VW implementation.
> Yes this is the idea. I hope the interface is good. 

The interface in base VW is, I'm afraid, not good, and should not be 
emulated. However, the WriteBarriers parcel, in preview in VW 7.7, is a 
start at a better API for this.

The basic problem is that the underlying VM "immutability" feature is 
useful for many things besides immutability. But the API is designed 
only for immutability, and using it for anything else is very ugly. It 
was probably a mistake to name the VM feature "immutability" in the 
first place. It's really "trap on write" and when you get a trap you can 
do many things -- reject the modification, conditionally allow it, 
notify then allow...



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