[Grace-core] "Classical" Inheritance for Grace

[Marco Servetto]

I have a bunch of comments:
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What are the semantics?  Hopefully what we (what most people) expect, what
we said above: we make a whole object, including all the methods &
unitialised fields, and then we run the code in all the class bodies
top-down, starting with the uppermost superclass (that had better not
inherit from anything). The result should be an initialized object.
* Initialisation:
  Defs have to be because they can't be initialised outside
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This is fundamentally broken. (and yes most of the oolanguages are broken
in this way): the initialization code in the parent class can call methods
overriden by the heir. This methods will unexpectedly find defs not
initialized.
Check out Hard-hat constructors.
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* Multiple inheritance
Can I please just assert this is orthogonal? We can do traits or ...
-------------------
You can at the price of having "classical inheritance" as the default way
to go and more expressive code combination pattern as a weird thing to do
in rare cases. If we want (trait, mixin or ...) code combination to be the
only composition, based on flattening, then "classical inheritance" is not
the "way to go". It is just a decision: we want a
-simple language with classical inheritance?
-simple language based on composition and flattening?
-a messy union of the two?
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Marco's placeholders... less powerful (w.r.t. newspeak futures): you
bind... raw identity to each name in a first pass, and then initialize all
the objects in a second pass.
... you cannot do *anything* to the objects until they are assigned, they
don't have any methods and you'd just get an "placeholder exception"
--------
the same limitation applied to nespeak futures:
But in a naive implementation, instead of a placeholder exception you *wait
forever* for the future to be completed....
A different discussion is "my typesystem" that indeed limits what you can
do.
But in a language where you accept the idea of having uninitialized field
exception on reading a field.... well.. placeholder exceptions are fine...

Marco.
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