I don't want stack once functions, because I feel that their use cases are
better served with RAII, which serves the same purposes without rightward drift
and without forcing LLVM to perform devirtualization.
Patrick
Oren Ben-Kiki <[email protected]> wrote:
>I find `do` syntax form is vital for DSL-ish code. Getting rid of it
>makes
>a lot of code look downright ugly. I'd rather it used a more Ruby-ish
>notation though, I find that putting the `do` far away from the `{ ...
>}`
>doesn't read well. `foo(....) do |...| { ... }` would have made more
>sense
>for me (think of `do` as a macro-ish binary operation injecting the
>proc
>into the function on the left). But the current form is acceptable.
>
>Syntax niceties aside, I find it extremely problematic that we have
>only
>two forms of "callable", one that is on the stack but can be called
>multiple times, and one that is on the heap and can only be called
>once.
>This arrangement sort-of-makes-sense when one thinks from an
>implementation
>point of view, but I find it to lack a crucial use case, that of a form
>that is on the stack and is also called only once.
>
>The reason this 3rd form is so important is the extremely common case
>of a
>container that wants to take an action as a parameter for a method.
>
>```
>... some_non_sendable_variable ...
>... some_owned_variable ...
>do container.do_something_at_most_once |...| { ... use *both* variables
>...
>}
>```
>
>This is a lose-lose situation. If the container takes a `proc`, then
>Rust
>complains that it can't capture the non-send-able variable. But if the
>container takes a stack closure, then Rust complains it can't use the
>owned
>variable. Of course, the container will _not_ send the action and will
>also
>_not_ call it twice, but it can't express this in the action type :-)
>The
>only workaround I found is to use a closure and wrap each and every
>non-send-able variable in a cell - this is an pointless and downright
>annoying manual boilerplate code.
>
>As long as this area of the language is being changed, I think that
>adding
>this missing 3rd variant should definitely be discussed (and hopefully
>implemented). This would affect the syntax discussion because there
>would
>be three forms instead of two; there are some more and less obvious
>choices
>here but they are secondary to the core issue of allowing the 3rd
>variant
>in the 1st place.
>
>On Sat, Nov 30, 2013 at 9:02 AM, Chris Morgan <[email protected]>
>wrote:
>
>> (a) Kill ``do``
>>
>...
>
>> (b) Make ``do`` support both closures and procedures
>>
>...
>
>
>------------------------------------------------------------------------
>
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