Re: What is your opinion on Global Objects?

[Stephen Leake <stephen_leake@stephe-leake.org>]

Adam Beneschan <adambeneschan@gmail.com> writes:

> On Thursday, November 20, 2014 8:34:31 AM UTC-8, Stephen Leake wrote:
>> 
>> > That basically is a vote for global objects. Whether they are accessed
>> > through a global variable or some sort of getter function that returns
>> > access, it means bypassing the parameters. Well from what I read here,
>> > there are no strong opinions for either concept. Strange, I wasn't
>> > able to find good arguments for or against the two concepts anywhere,
>> 
>> If you can really, truly, absolutely guarrantee that you will _never_
>> need two different copies of the data structure, then the singleton
>> pattern makes sense (data in a single variable in a package body).
>> 
>> If you ever need two different copies of the data structure, then you
>> need to pass it around in parameters.
>> 
>> The symbol table for a compiler is a good candidate for a singleton.
>
> This doesn't seem right to me.  
>
> I haven't followed the whole discussion closely, so I might have
> missed something... But in the case of a symbol table, an Ada compiler
> that implements generics by "macro instantiation" is an example of why
> a symbol table should *not* be a singleton. If the compiler rescans
> the text of the generic, the entire context (i.e. what symbols are
> visible) 

That's not the _entire_ symbol table, just one subtree.

I've never implemented a compiler, but I have implemented an
interpreter; it has a singleton symbol table.

I imagine "context" is a pointer into the symbol table, showing what is
visible at the current code position.

It certainly depends on how the compiler uses the symbol table.

-- 
-- Stephe