Thanks, I haven't seen that RFC before, but reading it now it seems it would be insufficient to support this use case without also supporting `let x: impl Future`, since the RFC deliberately chooses to expand to a temporary binding for `self`.
It would also appear to be deficient for the same parsing reason I mentioned, i.e. that you need some way to tell whether `2 + 2.bar!()` should expand to `2 + bar!(2)` or `bar!(2 + 2)`; the RFC appears to choose the latter, whereas a hypothetical `await!()` would want the former. This problem is called out in the RFC:
"Rather than this minimal approach, we could define a full postfix macro system that allows processing the preceding expression without evaluation. This would require specifying how much of the preceding expression to process unevaluated, including chains of such macros. Furthermore, unlike existing macros, which wrap around the expression whose evaluation they modify, if a postfix macro could arbitrarily control the evaluation of the method chain it postfixed, such a macro could change the interpretation of an arbitrarily long expression that it appears at the end of, which has the potential to create significantly more confusion when reading the code."
As far as I can see, the RFC doesn’t mention precedence at all, but I think it’s safe to assume that it’s meant to be the same as method calls. So `2 + 2.bar!()` would expand into something like
It would also appear to be deficient for the same parsing reason I mentioned, i.e. that you need some way to tell whether `2 + 2.bar!()` should expand to `2 + bar!(2)` or `bar!(2 + 2)`; the RFC appears to choose the latter, whereas a hypothetical `await!()` would want the former. This problem is called out in the RFC:
"Rather than this minimal approach, we could define a full postfix macro system that allows processing the preceding expression without evaluation. This would require specifying how much of the preceding expression to process unevaluated, including chains of such macros. Furthermore, unlike existing macros, which wrap around the expression whose evaluation they modify, if a postfix macro could arbitrarily control the evaluation of the method chain it postfixed, such a macro could change the interpretation of an arbitrarily long expression that it appears at the end of, which has the potential to create significantly more confusion when reading the code."