[Vm-dev] Re: [squeak-dev] The Trunk: System-eem.803.mcz

[Eliot Miranda]

Hi Tobias,

> On Mar 3, 2016, at 12:10 AM, Tobias Pape <Das.Linux at gmx.de> wrote:
> 
> 
> Hi all, Hi Eliot, Hi Clément
> 
> Well, you know I'm the opponent here regarding the Immutability naming.
> I hate that I have to come back to the naming thing here once again.
> But it is rather important for me, since I work on immutability concepts
> that are unlike what immutability would mean here. I think it is also
> important to know that immutability in most other languages means
> "it won't change whatsoever" (including OCaml[1], Racket[2], 
> Haskell[3], or object-oriented programming in general[4])
> 
> Now, I see the need, usefulness, and practical implementation for objects
> that cannot be written and hence throw an error, which _then_ can be
> circumvented/made be writable. I'm all for it and I like it. Except
> for the name.
> 
> As Clément put it:
>    "As argued on the virtual machine mailing list, we are talking 
>    about a write-barrier more than immutability itself."
> 
> 
> I would hence propose to name those objects
> 
>    locked objects
> 
> with the accompanying Someone-tries-to-write-that-Error named
> 
>    ObjectIsLockedError
> 
> and the state-change messages 
> 
>    Object>>lock
>    Object>>unlock
> 
> and likewise the VM-information
> 
>    SmalltalkImage>>supportsLockedObjects
> 
> I know, re-iterating this is tedious, but it will avoid unmet
> expectations by newcomers from other languages as well as
> name clashes with actual immutability implementations (how should
> we name those, then)?

No need to apologize.  I had forgotten the naming issue in my delight at fixing the actual VM issue and being able to get an immutability^h^h^h^h^h^h^h^h^h^h^h^hwrite-protect fault.  Forgive me.

But locked is definitely the wrong word.  To me it evokes notions of mutual exclusion and  concurrency.  Tomorrow I'll rename the accessors etc to use the term read-only, so supportsReadOnlyObjects, beReadOnly isReadOnly and setReadOnly:.  Ok with you?  Any objections y'all?

> 
> With apologies
>    -Tobias
> 
> 
> [1]: http://typeocaml.com/2015/01/02/immutable/
> [2]: a) http://docs.racket-lang.org/reference/pairs.html "Pairs are not mutable"
>     b) http://docs.racket-lang.org/reference/strings.html
> [3]: https://wiki.haskell.org/A_brief_introduction_to_Haskell#Immutable_declarations
> [4]: https://en.wikipedia.org/wiki/Immutable_object
> 
>> On 03.03.2016, at 03:19, commits at source.squeak.org wrote:
>> 
>> Eliot Miranda uploaded a new version of System to project The Trunk:
>> http://source.squeak.org/trunk/System-eem.803.mcz
>> 
>> ==================== Summary ====================
>> 
>> Name: System-eem.803
>> Author: eem
>> Time: 2 March 2016, 7:18:21.713694 pm
>> UUID: 934ce776-0717-469b-8818-300954393791
>> Ancestors: System-bf.802
>> 
>> Add getters that answer whether the VM supports immutability or multiple bytecode sets.
>> 
>> =============== Diff against System-bf.802 ===============
>> 
>> Item was added:
>> + ----- Method: SmalltalkImage>>supportsImmutability (in category 'system attributes') -----
>> + supportsImmutability
>> +    "Answer whether the VM observes the per-object immutability flag and consequently
>> +     aborts writes to inst vars of, and fails primitives that attempt to write, to immutable objects."
>> +    "SmalltalkImage current supportsImmutability"
>> + 
>> +    ^(self vmParameterAt: 65)
>> +        ifNil: [false]
>> +        ifNotNil:
>> +            [:param| "In older VMs this is a boolean reflecting MULTIPLE_BYTECODE_SETS"
>> +             param isInteger "In newer VMs it is a set of integer flags, bit 1 of which is IMMUTABILITY"
>> +                ifTrue: [param anyMask: 2]
>> +                ifFalse: [false]]!
>> 
>> Item was added:
>> + ----- Method: SmalltalkImage>>supportsMultipleBytecodeSets (in category 'system attributes') -----
>> + supportsMultipleBytecodeSets
>> +    "Answer whether the VM supports multiple bytecodeSets."
>> +    "SmalltalkImage current supportsMultipleBytecodeSets"
>> + 
>> +    ^(self vmParameterAt: 65)
>> +        ifNil: [false]
>> +        ifNotNil:
>> +            [:param| "In older VMs this is a boolean reflecting MULTIPLE_BYTECODE_SETS"
>> +             param isInteger "In newer VMs it is a set of integer flags, bit 0 of which is MULTIPLE_BYTECODE_SETS"
>> +                ifTrue: [param anyMask: 1]
>> +                ifFalse: [param]]!
>