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Note development roadmap
This page used to cover early (pre-0.1) tasks on the development roadmap for Rust. It is now an outline of where we plan to take the compiler over the course of the next several releases, ending in a 1.0 release that we commit to supporting over an extended time period. Where possible, we will link to bugs in the issue tracker.
Please note: when we do stabilize for a 1.0 release, it will not mean we are freezing the language for all time; it means we'll be branching and supporting a stable branch and a versioning strategy that "works" for an extended period (i.e. "years"), as well as committing to providing tools to help migrate code forward (help, not necessarily automate), when and if breaking changes are made in future versions.
Items on this page will move to the Doc detailed release notes page as they are completed.
See also [Note 0.5 priorities](Note 0.5 priorities)
(#2216) Loops currently cannot carry labels, which makes breaking from deep within a loop difficult. There's a pretty clear way to implement this, it just requires some care to avoid clashing with nearby syntax.
(#2755) This is a minor change that should effect no code presently; we'll be introducing a "raw string" form (possibly with a variety of legal delimiters) that does not balance the delimiter characters, so requires internal escaping of only the delimiter. This will replace the proposed (but never implemented) character-balanced custom lexeme syntax in the syntax-extension system. The cost of having a non-regular token grammar was deemed not worth the benefit, and most of the use cases for the latter are easily handled by the former.
(#3056) Closures have to encode their kind (whether they copy their environment, uniquely copy the unique parts, or only hold a safe reference to it). Currently this is indicated by a sigil: fn@ or fn~ or fn& or such. We're likely to change this to one of the kind names trailing the word fn. That is, call it fn:Copy or fn:Send.
(#3059) There is general consensus that floating point literals are too long; 1.0f will likely become sugar for 1.0f32. This is purely a backwards-compatible change. Alternately, we may extend integer literal inference to floats (#3059)
(#3061) Currently we have a full "language level" construct for a value-with-a-destructor: a drop block inside a struct. This is still more machinery than strictly necessary, and we wish to transition to merely interpreting the presence of a distinguished interface (intrinsic::drop) as indicative of a value having a destructor. All the same kind-related rules will apply, this is just a matter of removing surface machinery from the language.
(#2033) At the moment last-use analysis still drives injection of a substantial number of implicit unary move operators. This has proven too counter-intuitive to remain; at most we expect last-use analysis to drive a warning about large implicit copies, but nothing more.
(#2176) Crate files are at this point mostly an artifact of earlier beliefs that turned out not to be true (or convenient) in the compilation model. We believe they are now doing more harm than good, and their features can be presented as an "early pass" in the compilation model of a single tree of source files. Inter-file linkages will be given (within a crate) by the form mod foo = "path.rs".
(#1242 and #2119) The attribute system has served us well so far for conditional compilation but at times we find it not quite powerful enough. In particular, the ability to bind variables declaratively, as well as conditionally evaluate any attribute, seems lacking. We'll expand the attribute system to handle these cases, possibly changing its syntax slightly along the way.
(#2159 and #1772) For long-term source compatibility, we wish to make it possible (and in the case of packaged software for distribution via cargo, possibly mandatory) to tag rust source files with the language version they are written against. We'll be doing this outside the main lexical grammar, in a very simplified "pre-parse" grammar that we can expect to remain stable indefinitely. This sub-grammar is only enough to express version tags (though it uses a #-comment form that happens to overlap with the needs of #! at the first line of a file for running as a script).
(#2166) Currently a crate has a single version, which is mangled into all the symbols in the crate as well as the crate filename. This is not quite correct. What we want is a per-item version attribute (with a per-crate default) that is mangled into each symbol, but not the output filename, such that the compiler can tolerate compiling multiple versions of the same API inside a single output file. This should be mostly invisible to users.
0.3 will introduce an API for setting and retrieving task-local data. We'll build on top of this to provide dynamic-scoped variables (keyed by global constants), on top of that, condition-handlers that can be used to recover from errors at the site of the error, or else fail. This should hopefully address many of the remaining use-cases people have in mind for catchable exceptions.
The core::io library is due for a careful refactoring in terms of traits, condition handlers, and similar "new" abstractions that the language and libraries support. While this is true of the entire core and standard libraries, io is particularly important in our work due to its pervasive use and numerous implementation variants.
Once core::io is refactored, the std::serialization library will grow several more implementations, and once we decide on a preferred backend we'll migrate the compiler metadata tables to use it. This should be reasonably unnoticed by users, but will break binary compatibility between versions when we make the change.