Consider requiring optional dictionary defaulting explicitly

[annevk]

Instead of

foo(optional dictionaryType arg);

perhaps we should require writing

foo(optional dictionaryType arg = {});

for consistency with other optional arguments and for clarity for the reader. At least anecdotally this seems to be one of the most confusing things about IDL that's not a legacy feature.

[bzbarsky]

Or optional dictionaryType arg = null, though either one is probably ok... We just need to introduce new syntax to do = {}, last I checked, while = null should just work.

[annevk]

I suspect that = null might have the same problem and could even lead to prose that branches on null.

[bzbarsky]

OK. As long as people are clear on = {} meaning "empty dictionary", not "dictionary initialized from a {} JS object literal", since those are not the same thing...

[bzbarsky]

@annevk One question: would we still require the = {} on trailing (or all?) dictionary args to be present for the IDL to be valid? That seems generally desirable to me...

[annevk]

Yeah, I was thinking it would be a syntax error without it. I suspect we should require it always, to make it clear it's what happens when you pass undefined and you cannot branch on "dict not given" or some such.