Re: [Adobe-source-devel] View concept singleton state

[Ralph T. <ra...@gm...>]

I am also in favour of the first method, for the same reason, so long
as there is a way to register user defined types into the sheet (i.e.:
provide the string->type mapping).

Ralph

On 10/18/06, Sean Parent <sp...@ad...> wrote:
>
> On Oct 18, 2006, at 1:11 PM, Ralph Thomas wrote:
>
> > On 10/17/06, Mat Marcus <mm...@em...> wrote:
> >>  Sean said he would consider adding type constraints to the model.
> >
> > How would this work? What would happen if there was a type violation
> > -- would model throw an exception on set?
>
> There are several ways that I've been considering (but little time to
> explore) -
>
> One option is to add attributes to cells and add an analyze pass to
> the parser which would check for matching attributes and insert
> runtime checks where attributes can't be determined.
>
> Syntax for this would likely be along the lines of C/C++ except allow
> for multiple types.
>
> [number, string]  cell_name <== p ? "Hello" : 20; // OK
> [number] cell_name : "Hello"; // Parse Error
>
> Here the error would be reported as an exception. Ideally I could get
> the parser to construct the cell using a "type list" - this would
> look something like:
>
> add_interface_cell(@number, @std::string)(cell_name, initial_value);
>
> And the cell would be registered with these types. A bind that didn't
> match these types would fail with a cell not found. - There simply
> would not be a way to attach to a cell with a type mismatch (so a
> runtime error but on first connect). Using a type list interface on
> the bind side this could be statically enforced on the C++ code (so
> the client can't lie and claim to set a number but set a string):
>
> set<double>(cell_name, 10.5); // looks for cell matching [number]
> cell_name
>
> -----
>
> Another option is to do the type constraints as pure runtime checks:
>
> cell_name where((typeof(cell_name) == @number) && (cell_name < 10))
> <== 5; // OK
>
> This would be roughly equivalent to:
>
>         cell_name <== 5;
> invariant:
>         valid_cell <== (typeof(cell_name) == @number) && (cell_name < 10);
>
> This is more flexible but defers catching of errors to runtime -
> behavior of the check (throwing an exception vs. acting as an
> invariant) needs some thought and I have to play with use cases. I'm
> currently in favor of pursuing the first option as getting errors
> back as early as possible is a strong goal.
>
> Sean
>
>
> >
> > Ralph
> >
> > --
> > "i have a dream and it's called a crossbar switch/what this will mean
> > is no big data glitch"
> >
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