Hello!
> The first token in a YieldStatement production is always preceded by one of
> these separator tokens: ;, {, }, ), or ->.
Seems I'm missing something. Could you please illustrate in which case
YieldStatement could be preceded by ')'? Also what about '->'? In
lambda '->' is followed by an expression or block, but not a
statement. In switch '->' is followed by block, throw or expression
plus semicolon. Also could YieldStatement be preceded by ':' in old
switch format? E.g.
System.out.println(switch(0) { default: yield 1; }); // seems legit
Also sections 16.1.7 and 16.1.8 are named identically. Probably
there's some mistake.
With best regards,
Tagir Valeev.
On Fri, May 24, 2019 at 7:25 PM Gavin Bierman <[email protected]> wrote:
>
> A draft spec including the compromise strategy below is available at:
>
> http://cr.openjdk.java.net/~gbierman/jep354-jls-20190524.html
>
> Comments welcomed!
> Gavin
>
> On 22 May 2019, at 17:45, Brian Goetz <[email protected]> wrote:
>
> We’ve been drilling into the spec and implementation of yield as a contextual
> keyword. We have three possible strategies, all of which are specifiable and
> implementable, but with tradeoffs.
>
> The “dumb strategy” would be to say that `yield` is a keyword when it appears
> in the first position of a statement production (e.g., after an open brace or
> a semicolon.). This is simple to spec, and simple to implement, but it
> doesn’t so do well with variables named `yield`:
>
> yield++;
> yield = 3;
> if (foo)
> yield += 3;
> yield[3] = 4;
>
> The “smart strategy” says that `yield` is a keyword only within the context
> of the YieldStatement production; the rest of the time it is an identifier.
> This is also simple to spec, and does the right thing in all unambiguous
> cases, but requires unbounded lookahead, which compiler implementations may
> not like. The one ambiguous case is
>
> yield(e)
>
> which would match both YieldStatement and ExpressionStatement, and here we
> bias towards YieldStatement. Naked yield() invocations can qualify the
> invocation:
>
> this.yield(3)
> Thread.yield(4)
>
> The “compromise” strategy is like the smart strategy, except that it trades
> fixed lookahead for missing a few more method invocation cases. Here, we
> look at the tokens that follow the identifier yield, and use those to
> determine whether to classify yield as a keyword or identifier. (We’d choose
> identifier if it is an assignment op (=, +=, etc), left-bracket, dot, and a
> few others, plus a few two-token sequences (e.g., ++ and then semicolon),
> which is lookahead(2).
>
> The main difference between the compromise strategy and the smart strategy is
> the handling of method invocations that are not unary:
>
> yield(3, 4)
>
> In the smart strategy, we’d figure out that this is a method call; in the
> compromise strategy, we’d require qualification just as we do with the unary
> method.
>
> The compromise strategy misses some cases we could parse unambiguously, but
> also offers a simpler user model: always qualify invocations of methods
> called yield when used as expression statements. And it offers the better
> lookup behavior, which will make life easier for IDEs.
>
> So my recommendation here is the compromise strategy.
>
> On May 21, 2019, at 10:50 AM, Tagir Valeev <[email protected]> wrote:
>
> I discussed this with colleagues and can confirm that for IntelliJ
> IDEA parser it will be no problem to always consider yield as a
> statement. At least it's much easier than to consider it as a
> statement inside switchy blocks only.
>
> With best regards,
> Tagir Valeev.
>
> On Tue, May 21, 2019 at 12:38 PM Tagir Valeev <[email protected]> wrote:
>
>
> So does this (option B plus your No) mean that IDEs would tend to color
> "yield" as a keyword (at the beginning of a statement) even if followed by
> "("?
>
>
> My "No" was mostly against options C and D where symbol resolution
> affects the parse tree. Sorry if it wasn't clear from my message. When
> the context for the parsing is available inside the same Java file,
> it's usually ok. See the 'var' restricted keyword:
>
> var var = 10; // first is highlighted as type, second as local variable
> var = 20; // var is highlighted as local variable, despite it's at the
> beginning of a statement.
> var(1); // var is highlighted as a method call, despite it's at the
> beginning of a statement.
>
> We have no very big problems parsing this.
>
> With best regards,
> Tagir Valeev.
>
> On Tue, May 21, 2019 at 2:52 AM John Rose <[email protected]> wrote:
>
>
> On May 20, 2019, at 8:24 AM, Tagir Valeev <[email protected]> wrote:
>
>
> Assuming that we agreed on 'yield' the option B seems the most attractive. A
> big No to context-specific parse tree. It's a complete pain to IDEs. Don't
> forget that IDE often deals with incomplete code, missing dependencies, etc.,
> and still needs to provide reasonable highlighting and completion. Imagine
> that 'yield' method is available via import static Foo.* or superclass. In
> this case we don't want to look into other files to build a correct parse
> tree.
>
>
> So does this (option B plus your No) mean that IDEs would
> tend to color "yield" as a keyword (at the beginning of a
> statement) even if followed by "("?
>
> I suppose that would work. It's hard to predict what that
> would feel like, but it's logical.
>
> — John
>
>
>
