I decided to split this out to its own thread because it seems orthogonal to
other issues being discussed.
When I read this line from the proposal:
await decodeImage(dataResource.get(), imageResource.get())
It’s not clear to me where the asynchronous call is. There are three function
calls on that line. Which ones might actually suspend? You can’t tell by
looking at it because there’s only one await keyword (the answer is all 3).
I’m not a fan of the ambiguity of applying the await keyword to an entire
statement. I know some people think this is a good thing, but to me it’s just
obfuscating important information.
Further, if you’re going beyond a single expression then why you would stop at
the statement level? Why not make it apply to the whole block or even a whole
function? Why require the keyword at all? It doesn’t appear to be adding any
value if it doesn’t specify exactly where the suspension point is. “Somewhere
on this line” can get rather vague.
async/await can be a huge win for clarity, but it also comes with the downside
of having to think a bit more about what can happen at these suspension points.
I feel like it should be a goal to make it very clear where those suspension
points are so that we can more easily reason about them. That’s why I prefer
restricting it to apply to a single expression. It’s very clear where the
function gets suspended, which means it’s clearer where you need to be
concerned about things possibly happening in between your code. Consider this,
for example:
await decodeImage(loadWebResource(self.webProfilePath),
loadWebResource(self.imagePath))
If webProfilePath and imagePath are vars then they could change in between
those two calls. If you can’t see that these calls are suspending then you
might not know to cache them up-front to ensure consistency:
let webProfilePath = self.webProfilePath
let imagePath = self.imagePath
await decodeImage(await loadWebResource(webProfilePath), await
loadWebResource(imagePath))
I think a general guideline we should use when considering how this feature
should work is to ask whether it makes bugs more likely or less likely. The
goal should be to reduce bugs while simplifying code. If we simplify the code
to the point where we’re making some bugs too subtle then we may be doing more
harm than good.
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