bors f9fc49c06e auto merge of #17853 : alexcrichton/rust/issue-17718, r=pcwalton
This change is an implementation of [RFC 69][rfc] which adds a third kind of
global to the language, `const`. This global is most similar to what the old
`static` was, and if you're unsure about what to use then you should use a
`const`.

The semantics of these three kinds of globals are:

* A `const` does not represent a memory location, but only a value. Constants
  are translated as rvalues, which means that their values are directly inlined
  at usage location (similar to a #define in C/C++). Constant values are, well,
  constant, and can not be modified. Any "modification" is actually a
  modification to a local value on the stack rather than the actual constant
  itself.

  Almost all values are allowed inside constants, whether they have interior
  mutability or not. There are a few minor restrictions listed in the RFC, but
  they should in general not come up too often.

* A `static` now always represents a memory location (unconditionally). Any
  references to the same `static` are actually a reference to the same memory
  location. Only values whose types ascribe to `Sync` are allowed in a `static`.
  This restriction is in place because many threads may access a `static`
  concurrently. Lifting this restriction (and allowing unsafe access) is a
  future extension not implemented at this time.

* A `static mut` continues to always represent a memory location. All references
  to a `static mut` continue to be `unsafe`.

This is a large breaking change, and many programs will need to be updated
accordingly. A summary of the breaking changes is:

* Statics may no longer be used in patterns. Statics now always represent a
  memory location, which can sometimes be modified. To fix code, repurpose the
  matched-on-`static` to a `const`.

      static FOO: uint = 4;
      match n {
          FOO => { /* ... */ }
          _ => { /* ... */ }
      }

  change this code to:

      const FOO: uint = 4;
      match n {
          FOO => { /* ... */ }
          _ => { /* ... */ }
      }

* Statics may no longer refer to other statics by value. Due to statics being
  able to change at runtime, allowing them to reference one another could
  possibly lead to confusing semantics. If you are in this situation, use a
  constant initializer instead. Note, however, that statics may reference other
  statics by address, however.

* Statics may no longer be used in constant expressions, such as array lengths.
  This is due to the same restrictions as listed above. Use a `const` instead.

[breaking-change]
Closes #17718 

[rfc]: https://github.com/rust-lang/rfcs/pull/246
2014-10-10 00:07:08 +00:00
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This is a preliminary version of the Rust compiler, libraries and tools.

Source layout:

Path Description
librustc/ The self-hosted compiler
liballoc/ Rust's core allocation library
libcore/ The Rust core library
libdebug/ Debugging utilities
libstd/ The standard library (imported and linked by default)
libgreen/ The M:N runtime library
libnative/ The 1:1 runtime library
libsyntax/ The Rust parser and pretty-printer
libtest/ Rust's test-runner code
------------------- ---------------------------------------------------------
libarena/ The arena (a fast but limited) memory allocator
libbacktrace/ The libbacktrace library
libcollections/ A collection of useful data structures and containers
libflate/ Simple compression library
libfmt_macros/ Macro support for format strings
libfourcc/ Data format identifier library
libgetopts/ Get command-line-options library
libglob/ Unix glob patterns library
libgraphviz/ Generating files for Graphviz
libhexfloat/ Hexadecimal floating-point literals
liblibc/ Bindings for the C standard library
liblog/ Utilities for program-wide and customizable logging
libnum/ Extended number support library (complex, rational, etc)
librand/ Random numbers and distributions
libregex/ Regular expressions
libregex_macros/ The regex! syntax extension
libsemver/ Rust's semantic versioning library
libserialize/ Encode-Decode types library
libsync/ Concurrency mechanisms and primitives
libterm/ ANSI color library for terminals
libtime/ Time operations library
liburl/ URL handling lirary
libuuid/ UUID's handling code
------------------- ---------------------------------------------------------
rt/ The runtime system
rt/rust_*.c - Some of the runtime services
rt/vg - Valgrind headers
rt/msvc - MSVC support
rt/sundown - The Markdown library used by rustdoc
------------------- ---------------------------------------------------------
compiletest/ The test runner
test/ Testsuite
test/codegen - Tests for the LLVM IR infrastructure
test/compile-fail - Tests that should fail to compile
test/debug-info - Tests for the debuginfo tool
test/run-fail - Tests that should compile, run and fail
test/run-make - Tests that depend on a Makefile infrastructure
test/run-pass - Tests that should compile, run and succeed
test/bench - Benchmarks and miscellaneous
test/pretty - Pretty-printer tests
test/auxiliary - Dependencies of tests
------------------- ---------------------------------------------------------
librustdoc/ The Rust API documentation tool
------------------- ---------------------------------------------------------
llvm/ The LLVM submodule
rustllvm/ LLVM support code
------------------- ---------------------------------------------------------
etc/ Scripts, editors support, misc

NOTE: This list (especially the second part of the table which contains modules and libraries) is highly volatile and subject to change.