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overloaded-box and placement-in #809

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merged 11 commits into from
Feb 11, 2015
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overloaded-box and placement-in #809

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3927d56
initial draft
pnkfelix Feb 4, 2015
a980f3d
mention more about alternative syntax.
pnkfelix Feb 5, 2015
c081b93
add new drawback based on observing inference weakness for `Box<Trait>`.
pnkfelix Feb 5, 2015
10388e0
switched placement-`in` syntax to `in PLACE { BLOCK }`.
pnkfelix Feb 9, 2015
28a30fb
Extend Drawbacks section's discussion of type-inference and coercion
pnkfelix Feb 9, 2015
9f4b6e8
Added more complete example of drawback, taken from gists on PR 22086.
pnkfelix Feb 9, 2015
4ca4bd0
add transcript of compilation attempts, so the reader can see concretely
pnkfelix Feb 9, 2015
9d53797
Add one more note about acription and a place where it is particularly
pnkfelix Feb 9, 2015
4ec9be7
Add notes on using distinct feature-names for gating the two syntaxes…
pnkfelix Feb 9, 2015
f6df740
Note potential reason to keep `in (<place>) <expr>` over `in <place> …
pnkfelix Feb 9, 2015
2880173
Decided I care enough about the overloading+inference+coercion question
pnkfelix Feb 9, 2015
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mention more about alternative syntax.
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pnkfelix committed Feb 5, 2015
commit a980f3d2b4fe110a34dde39b0fad9b9ee603d121
20 changes: 20 additions & 0 deletions text/0000-box-and-in-for-stdlib.md
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Expand Up @@ -129,6 +129,26 @@ tandem with types provided by the stdlib, such as `Box<T>`.
some integration with `box` pattern syntax that would motivate using
the `box` keyword for placement.

* A number of other syntaxes for placement have been proposed in the
past; see for example discussion on [RFC PR 405] as well as
[the previous placement RFC][RFC Surface Syntax Discussion].

The main constraints I want to meet are:
1. Do not introduce ambiguity into the grammar for Rust
2. Maintain left-to-right evaluation order (so the place should
appear to the left of the value expression in the text).

But otherwise I am not particularly attached to any single
syntax.

One particular alternative that might placate those who object
to placement-`in`'s `box`-free form would be:
`box (in <place-expr>) <expr>`.

[RFC PR 405]: /~https://github.com/rust-lang/rfcs/issues/405

[RFC Surface Syntax Discussion]: /~https://github.com/pnkfelix/rfcs/blob/fsk-placement-box-rfc/text/0000-placement-box.md#same-semantics-but-different-surface-syntax

* Do nothing. I.e. do not even accept an unstable libstd-only protocol
for placement-`in` and overloaded-`box`. This would be okay, but
unfortunate, since in the past some users have identified
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