Prevent cloning of clones

[Adde]

Brian Rice wrote:

>
> On Apr 26, 2005, at 11:50 AM, Adde wrote:
>
>> Thanks! I was just trying to understand when and how to limit further 
>> cloning.
>> Following your suggestions i came up with the following:
>>
>> SVG ensureDelegatedNamespace: #Units.
>> SVG Units addImmutableSlot: #Pixel valued: (BaseUnit name: 'pixel' 
>> abbrev: 'px').
>>
>> n@(Number traits) px [
>>  n with: px
>> ].
>>
>> uv@(UnitValue traits) toXML [
>>  (uv value toXML) ; (uv unit abbrev toXML)
>> ].
>>
>> s@(String traits) toXML [
>> s
>> ].
>>
>> n@(Number traits) toXML [
>>  n as: String
>> ].
>
>
> Interesting.
>
>> I added the px method to Number traits to be able to say: 1 px 
>> instead of 1 with: px, don't know if that's a good idea but it 
>> certanly makes it easier to use. The other methods are just 
>> placeholder for XML-specific formatting.
>
>
> The "px" message idea has occurred to me before, and I think what I'll 
> do is have the BaseUnit creation method name:abbrev: create the method 
> for you so you don't have to do it. How does that sound? :)

Sounds great!

>
>> I plan on changing the toXML methods into printOn: s@(XMLStream) to 
>> match the rest of the environment better.
>
>
> Cool. You can also do "XML WriteStream" or "XML Document WriteStream" 
> or also use "nextPut:" and override per type.
>
I'll look into it, though I'm sure I'll have to pester you some more 
about it before I get it to work ;)
Are there any examples in the library that I can look at?

>> I feel a bit unsure about the method on UnitValue traits, it feels 
>> like I should only provide toXML for my own UnitValues, something 
>> like this:
>>
>> SVG addPrototype: #Unit derivedFrom: {BaseUnit}.
>> SVG Unit addImmutableSlot: #Pixel valued: (SVG Unit name: 'pixel' 
>> abbrev: 'px').
>> SVG addPrototype: #UnitValue derivedFrom: {UnitValue}.
>>
>> uv@(UnitValue traits) unit: u@(SVG Unit traits) value: v [
>>  SVG UnitValue clone `>> [unit: u. value: v.]
>> ].
>>
>> uv@(SVG UnitValue traits) toXML [
>>  (uv value toXML) ; (uv unit abbrev toXML)
>> ].
>>
>> At least that works as it should, "(1 px) toXML" works and "(1 kg) 
>> toXML" gives an error.
>
>
> I don't think this is worthwhile; my recommendation is just to shift 
> from toXML to the nextPut: overriding and deal with it then. You're 
> basically programming over-defensively, since lengths may also count 
> as SVG units.
>
> I should mention one issue, though: pixels are not specific to SVG; 
> they're specific to the raster display type. Try to just keep it as 
> "yet another unit" which will be in the units namespace, and not 
> hardcode it as belonging to SVG. I say this because SVG is 
> conceptually a particular rendering backend for the UI framework (see 
> src/ui/) and as such I will want to have it not duplicate any structures.
>
It's highly likely that this is just me programming over-defensively. 
I've spent a considerable part of my life trying to please C++.
But, I feel that the only Units that should be used with toXML are Units 
for which someone has specified an XML representation (overridden 
toXML). Lengths counts as SVG units the second someone specifies how a 
Length should be formatted in in an SVG Document.
This feels like a problem that's bound to come up again, that you wan't 
to add special formatting to specific kinds of Units (instead of adding 
it to BaseUnit).
I fully agree that the Pixel unit probably belongs in some kind of 
Graphics namespace, though.

>> I have to say the language feels good so far, it strikes a fine 
>> balance between the beauty of Smalltalk and the raw power of Lisp.
>
>
> Cool, thanks!
>
>> Brian Rice wrote:
>>
>>> On Apr 25, 2005, at 1:43 PM, Brian Rice wrote:
>>>
>>>> I strongly suggest that you just forget about this issue and don't 
>>>> worry about the safety factor for now. Focus on the real design 
>>>> issues first; your code is a mess and is not re-using the very 
>>>> useful library I mentioned above. Try this instead:
>>>>
>>>> load: 'src/lib/dimensioned.slate'.
>>>> SVG addImmutableSlot: #Pixel valued: (BaseUnit name: 'pixel' 
>>>> abbrev: 'px').
>>>>
>>>> Doesn't that look better? It also can be used for actual algebraic 
>>>> operations, e.g.:
>>>>
>>>> Slate> BaseUnit name: 'pixel' abbrev: 'px'.
>>>> px
>>>> Slate> 4 with: pixel.
>>>> 4_px
>>>> Slate> it * 5.
>>>> 20_px
>>>> Slate> it / (1 with: in).
>>>> 20_px/in
>>>
>>>
>>> And if you define:
>>>
>>> x@(UnitValue traits) / y@(Unit traits)
>>> [x / (1 with: y)].
>>>
>>> Then "(72 with: px) / in" works. I'll add that now to the main 
>>> source tree.
>>>
>>>> The underscores are not really suitable for output into XML, but 
>>>> you can easily do something different there, or we could fix the 
>>>> print-out or provide some other means. In any case, you have 
>>>> multi-dispatch and can handle the case specifically in any output 
>>>> method.
>>>
> -- 
> Brian T. Rice
> LOGOS Research and Development
> http://tunes.org/~water/
>