A method that tests for "is running Cog" and that blows up if you are not
running Cog is not a very sensible thing. If you can make it faster and
prettier that's great, but please do check to make sure it actually works.

Dave

> I'm not one to tread into you VM guys' domain but I just wanted to
> express my agreement with Eliot.  "Performance" isn't the only viable
> criticism of using on: Error do: [ ... ].  It's just plain bad style,
> bad code.  We know better than to do that.
>
>
> On Mon, Sep 8, 2014 at 1:58 PM, Bert Freudenberg <bert at freudenbergs.de>
> wrote:
>> On 08.09.2014, at 20:45, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>>
>> On Sun, Sep 7, 2014 at 1:58 PM, <commits at source.squeak.org> wrote:
>>>
>>> David T. Lewis uploaded a new version of System to project The Trunk:
>>> http://source.squeak.org/trunk/System-dtl.685.mcz
>>>
>>> ==================== Summary ====================
>>>
>>> Name: System-dtl.685
>>> Author: dtl
>>> Time: 7 September 2014, 4:58:15.377 pm
>>> UUID: 55eba121-23d3-41cc-9525-52554adac2ec
>>> Ancestors: System-eem.684
>>>
>>> Smalltalk isRunningCog should answer false for an interpreter VM
>>>
>>> =============== Diff against System-eem.684 ===============
>>>
>>> Item was changed:
>>>   ----- Method: SmalltalkImage>>isRunningCog (in category 'system
>>> attributes') -----
>>>   isRunningCog
>>>         "Answers if we're running on a Cog VM (JIT or
>>> StackInterpreter)"
>>>
>>> +       ^( [self vmParameterAt: 42] on: Error do: [] )
>>> -       ^(self vmParameterAt: 42)
>>>                 ifNil: [false]
>>>                 ifNotNil: [:numStackPages| numStackPages > 0]!
>>
>>
>> Instead of creating an exception handler why not modify the interpreter
>> to
>> answer nil?  I know the answer is that the Interpreter doesn't, and
>> fails.
>> But we've had years in which we could change the Interpreter to match
>> vmParameterAt: and instead of doing the good thing (have the Interpreter
>> answer nil for values answered by Cog VMs), we force the standard system
>> to
>> waste time.  We should optimize the common case (trunk running on Cog)
>> not
>> penalize it to cover the uncommon case (trunk running on Interpreter
>> VM).
>>
>>
>> Nah, if performance really was an issue we could just remove the
>> primitiveFailed in vmParameterAt:. No need to change the VM.
>>
>> - Bert -
>>
>>
>>
>>
>>
>>
>