reflection (was: embedding based prototype languages)

Jecel Assumpcao Jr jecel at
Fri Nov 8 22:18:03 UTC 2002

On Friday 08 November 2002 17:35, James McCartney wrote:
> In Self this operation is considered reflective, but I'm not sure
> why. I would consider assigning methods to slots to be a normal kind
> of operation. It is a more specific way to change behaviour than
> dynamic inheritance via assigning parents, which I would think would
> be the more reflective operation.

Methods are considered constants in Self. If I have an object like this:

           ( | a <- 3. b = 4 | )

then changing the value of "a" can be done with a simple message send 
and is considered "normal programming", while changing the value of "b" 
requires either a primitive (_AddSlots:) or using a mirror on this 
object, either of which would be considered "meta programming".

So though both "a" and "b" can be changed, having to programmer 
explicitly give the system a tip about how they probably will be used 
allows the compiler to do a better job. So does having all method slots 
be constant.

One change in Self 4.1.6 compared to previous releases is that now you 
have the option of storing method objects in data slots.

One complication of having assignable method slots is that though 
assignment is unambiguous enough, what happens when you read from the 
slot? Do you get the method object as the result or is the method 
automatically executed? No matter which one you choose as the default, 
you will need a special scheme for the other.

In another email James McCartney wrote:
> But those authors pack their tables in the paper I read. In fact I use 
> exactly their selector based row displacement packing technique in my 
> own vm.

The paper I mentioned can be found at
though for some reason I can't access that right now.

All compression schemes require you to add some extra tests to your 
dispatch sequence. Normally it is well worth it. But I have a machine 
running at 57MHz with lots of extra memory that I can't otherwise use, 
so I don't compress.

-- Jecel

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