On Nov 22, 2010, at 12:37 AM, Peter van der Zee wrote:
> On Mon, Nov 22, 2010 at 6:54 AM, Brendan Eich <[email protected]> wrote:
>
> The ML-ish solution, which is forward compatible, is to parenthesize:
>
> let typedObj = { (prop1:type1): value1, (prop2:type2): value2, ... };
>
> The parentheses hurt too, but only this case. And it still may win to
> annotate the entire ObjectLiteral sometimes, which would avoid (or move to
> one common guard-type definition) the property-wise annotation overhead.
> Comments?
>
> I wouldn't want to introduce forced parens for the sake of disambiguation for
> the coder. I'd rather go with ::, # or @ ...
Those are not all equally good, and you're again sacrificing the common case
(especially with ::) where there's no need to parenthesize, for the uncommon
case of property-wise type annotation in an object initialiser.
Actually, one can use : just fine in an initialiser provided one or two colons
are required per property initialiser. There's no need for :: or anything else
except to avoid a confusing re-use of colon. Which is an issue, but :: doesn't
exactly address it!
Fundamenally, though, you have to weight each use-case by frequency. If as I
argue var x : T, function f(a: T, b: U): V {...}, etc. annotations dominate the
rare var typedObj = ... case, then parens or whatever is needed (even a
separated type annotation for the whole initialiser, as in ES4) is worth it.
> Actually, for object literal I'd go for an equal sign (=), but that obviously
> won't fix var declarations where the colon is fine.
We're not changing object initialiser syntax.
> Can't the guards proposal be applied to function parameters as well? Or am I
> stepping on land mines there? :) It seems like the same logic could be
> applied. In that case the equal sign is maybe even more preferable.
What are you proposing = be used for, if not default parameter values (see the
wiki) or assignment? No way does = make sense for type annotation.
But yes: type annotation (guard, contract, whateve -- not static types but
that's not at issue) should be possible for function parameters, return types,
local variables, let bindings, catch vars, etc.
/be
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