Julia v0.5.0 Release Notes
==========================

New language features
---------------------

  * Generator expressions, e.g. `f(i) for i in 1:n` ([#4470]). This returns an iterator
    that computes the specified values on demand.

  * Broadcasting syntax: ``f.(args...)`` is equivalent to ``broadcast(f, args...)`` ([#15032]).

  * Macro expander functions are now generic, so macros can have multiple definitions
    (e.g. for different numbers of arguments, or optional arguments) ([#8846], [#9627]).
    However note that the argument types refer to the syntax tree representation, and not
    to the types of run time values.

  * Varargs functions like `foo{T}(x::T...)` may now restrict the number
    of such arguments using `foo{T,N}(x::Vararg{T,N})` ([#11242]).

  * `x ∈ X` is now a synonym for `x in X` in `for` loops and comprehensions,
    as it already was in comparisons ([#13824]).

  * `PROGRAM_FILE` global is now available for determining the name of the running script ([#14114]).

  * The syntax `x.:sym` (e.g. `Base.:+`) is now supported, and `x.(:sym)` is deprecated ([#15032]).

  * Function return type syntax `function f()::T` has been added ([#1090]). Values returned
    from a function with such a declaration will be converted to the specified type `T`.

  * Experimental support for arrays with indexing starting at values
    different from 1. The array types are expected to be defined in
    packages, but now Julia provides an API for writing generic
    algorithms for arbitrary indexing schemes ([#16260]).

Language changes
----------------

  * Each function and closure now has its own type. The captured variables of a closure
    are fields of its type. `Function` is now an abstract type, and is the default supertype
    of functions and closures. All functions, including anonymous functions,
    are generic and support all features (e.g. keyword arguments).
    Instead of adding methods to `call`, methods are added by type using the syntax
    `(::ftype)(...) = ...`. `call` is deprecated ([#13412]).

  * `using` and `import` are now case-sensitive even on case-insensitive filesystems (common on Mac and Windows) ([#13542]).

  * Relational symbols are now allowed as infix operators ([#8036]).

  * A warning is always given when a method is overwritten (previously, this was done only when the new
    and old definitions were in separate modules) ([#14759]).

  * `A <: B` is parsed as `Expr(:(<:), :A, :B)` in all cases ([#9503]). This also applies to the
    `>:` operator.

  * Simple 2-argument comparisons like `A < B` are parsed as calls instead of using the
    `:comparison` expression type.

  * The `if` keyword cannot be followed immediately by a line break ([#15763]).

  * The built-in `NTuple` type has been removed; `NTuple{N,T}` is now
    implemented internally as `Tuple{Vararg{T,N}}` ([#11242]).

Command-line option changes
---------------------------

Compiler/Runtime improvements
-----------------------------

  * Machine SIMD types can be represented in Julia as a homogeneous tuple of `VecElement` ([#15244]).

Breaking changes
----------------

  * Method ambiguities no longer generate warnings when files are
    loaded, nor do they dispatch to an arbitrarily-chosen method;
    instead, a call that cannot be resolved to a single method results
    in a `MethodError`. ([#6190])

  * `pmap` keyword arguments `err_retry=true` and `err_stop=false` are deprecated.
    Action to be taken on errors can be specified via the `on_error` keyword argument.
    Retry is specified via `retry_n`, `retry_on` and `retry_max_delay`.

  * `reshape` is now defined to always share data with the original array.
    If a reshaped copy is needed, use `copy(reshape(a))` or `copy!` to a new array of
    the desired shape ([#4211]).

  * `mapslices` will always pass a view, so passing mutating functions will mutate the underlying array ([#16260])

  * Local variables and arguments are represented in lowered code as numbered `Slot`
    objects instead of as symbols ([#15609]).

  * The information that used to be in the `ast` field of the `LambdaStaticData` type
    is now divided among the fields `code`, `slotnames`, `slottypes`, `slotflags`,
    `gensymtypes`, `rettype`, `nargs`, and `isva` in the `LambdaInfo` type ([#15609]).

  * Juxtaposition of numeric literals ending in `.` (e.g. `1.x`) is no longer
    allowed ([#15731]).

Library improvements
--------------------

  * Strings ([#16107]):

    * The `UTF8String` and `ASCIIString` types have been merged into a single
      `String` type ([#16058]).  Use `isascii(s)` to check whether
      a string contains only ASCII characters.

    * The basic string construction routines are now `string(args...)`,
      `String(s)`, `unsafe_string(ptr)` (formerly `bytestring(ptr)`), and
      `unsafe_wrap(String, ptr)` (formerly `pointer_to_string`) ([#16731]).

  * Most of the combinatorics functions have been moved from `Base`
    to the [Combinatorics.jl package](https://github.com/JuliaLang/Combinatorics.jl) ([#13897]).

  * Packages:

    * The package system (`Pkg`) is now based on the `libgit2` library, rather
      than running the `git` program, increasing performance (especially on
      Windows) ([#11196]).

    * Package-development functions like `Pkg.tag` and `Pkg.publish`
      have been moved to an external [PkgDev] package ([#13387]).

  * The `Base.Test` module now has a `@testset` feature to bundle
    tests together and delay throwing an error until the end ([#13062]).

    * The new features are mirrored in the
      [BaseTestNext](https://github.com/IainNZ/BaseTestNext.jl)
      package for users who would like to use the new functionality on Julia v0.4.

    * The [BaseTestDeprecated](https://github.com/IainNZ/BaseTestDeprecated.jl)
      package provides the old-style `handler` functionality, for compatibility
      with code that needs to support both Julia v0.4 and v0.5.

  * The functions `remotecall`, `remotecall_fetch`, and `remotecall_wait` now have the
    function argument as the first argument to allow for do-block syntax ([#13338]).

  * `cov` and `cor` don't use keyword arguments anymore and are therefore now type stable ([#13465]).

  * Arrays and linear algebra:

    * All dimensions indexed by scalars are now dropped, whereas previously only
      trailing scalar dimensions would be omitted from the result ([#13612]).

    * Dimensions indexed by multidimensional arrays add dimensions. More generally, the dimensionality of the result is the sum of the dimensionalities of the indices ([#15431]).

    * New `normalize` and `normalize!` convenience functions for normalizing
      vectors ([#13681]).

    * QR

      * New method for generic QR with column pivoting ([#13480]).

      * New method for polar decompositions of `AbstractVector`s ([#13681]).

    * A new `SparseVector` type allows for one-dimensional sparse arrays.
      Slicing and reshaping sparse matrices now return vectors when
      appropriate. The `sparsevec` function returns a one-dimensional sparse
      vector instead of a one-column sparse matrix. ([#13440])

    * Rank one update and downdate functions, `lowrankupdate`, `lowrankupdate!`, `lowrankdowndate`,
    and `lowrankdowndate!`, for dense Cholesky factorizations ([#14243], [#14424])

    * All `sparse` methods now retain provided numerical zeros as structural nonzeros; to
      drop numerical zeros, use `dropzeros!` ([#14798], [#15242]).

  * New `foreach` function for calling a function on every element of a collection when
    the results are not needed.

  * `Cmd(cmd; ...)` now accepts new Windows-specific options `windows_verbatim`
    (to alter Windows command-line generation) and `windows_hide` (to
    suppress creation of new console windows) ([#13780]).

  * Statistics:

    * Improve performance of `quantile` ([#14413]).

    * `extrema` can now operate over a region ([#15550]).

  * The new `Base.StackTraces` module makes stack traces easier to use programmatically ([#14469]).

  * There is now a default no-op `flush(io)` function for all `IO` types ([#16403]).

  * Concatenating dense and sparse matrices now returns a sparse matrix ([#15172]).

  * The `libjulia` library is now properly versioned and installed to the public `<prefix>/lib`
    directory, instead of the private `<prefix>/lib/julia` directory ([#16362]).

  * System reflection is now more consistently exposed from Sys and not Base.
    `OS_NAME` has been replaced by `Sys.KERNEL` and always reports the name of the kernel (as reported by `uname`).
    The `@windows_only` and `@osx` family of macros have been replaced with functions such as `is_windows()` and
    or `is_apple()`. There's now also an `@static` macro that will evaluate the condition of an if-statement at
    compile time, for when a static branch is required ([#16219]).

  * Prime number related functions have been moved from `Base` to the
    [Primes.jl package](https://github.com/JuliaMath/Primes.jl) ([#16481]).

Deprecated or removed
---------------------

  * The following function names have been simplified and unified ([#13232]):

    * `get_bigfloat_precision`  -> `precision(BigFloat)`
    * `set_bigfloat_precision`  -> `setprecision`
    * `with_bigfloat_precision` -> `setprecision`

    * `get_rounding`            -> `rounding`
    * `set_rounding`            -> `setrounding`
    * `with_rounding`           -> `setrounding`

  * The method `A_ldiv_B!(SparseMatrixCSC, StrideVecOrMat)` has been deprecated
    in favor of versions that require the matrix to be in factored form
    ([#13496]).

  * Deprecate `chol(A,Val{:U/:L})` in favor of `chol(A)` ([#13680]).

  * `issym` is deprecated in favor of `issymmetric` to match similar functions (`ishermitian`, ...) ([#15192])

  * `scale` is deprecated in favor of either `α*A`, `Diagonal(x)*A`, or `A*Diagonal(x)`. ([#15258])

  * `xdump` is removed, and `dump` now simply shows the full representation of a value.
    `dump` should not be overloaded, since it is for examining concrete structure ([#4163]).

  * `sub` and `slice` have been deprecated in favor of `view` ([#16972])

[PkgDev]: https://github.com/JuliaLang/PkgDev.jl
<!--- generated by NEWS-update.jl: -->
[#1090]: https://github.com/JuliaLang/julia/issues/1090
[#4163]: https://github.com/JuliaLang/julia/issues/4163
[#4211]: https://github.com/JuliaLang/julia/issues/4211
[#4470]: https://github.com/JuliaLang/julia/issues/4470
[#6190]: https://github.com/JuliaLang/julia/issues/6190
[#8036]: https://github.com/JuliaLang/julia/issues/8036
[#8846]: https://github.com/JuliaLang/julia/issues/8846
[#9503]: https://github.com/JuliaLang/julia/issues/9503
[#9627]: https://github.com/JuliaLang/julia/issues/9627
[#11196]: https://github.com/JuliaLang/julia/issues/11196
[#11242]: https://github.com/JuliaLang/julia/issues/11242
[#13062]: https://github.com/JuliaLang/julia/issues/13062
[#13232]: https://github.com/JuliaLang/julia/issues/13232
[#13338]: https://github.com/JuliaLang/julia/issues/13338
[#13387]: https://github.com/JuliaLang/julia/issues/13387
[#13412]: https://github.com/JuliaLang/julia/issues/13412
[#13440]: https://github.com/JuliaLang/julia/issues/13440
[#13465]: https://github.com/JuliaLang/julia/issues/13465
[#13480]: https://github.com/JuliaLang/julia/issues/13480
[#13496]: https://github.com/JuliaLang/julia/issues/13496
[#13542]: https://github.com/JuliaLang/julia/issues/13542
[#13612]: https://github.com/JuliaLang/julia/issues/13612
[#13680]: https://github.com/JuliaLang/julia/issues/13680
[#13681]: https://github.com/JuliaLang/julia/issues/13681
[#13780]: https://github.com/JuliaLang/julia/issues/13780
[#13824]: https://github.com/JuliaLang/julia/issues/13824
[#13897]: https://github.com/JuliaLang/julia/issues/13897
[#14114]: https://github.com/JuliaLang/julia/issues/14114
[#14243]: https://github.com/JuliaLang/julia/issues/14243
[#14413]: https://github.com/JuliaLang/julia/issues/14413
[#14424]: https://github.com/JuliaLang/julia/issues/14424
[#14469]: https://github.com/JuliaLang/julia/issues/14469
[#14759]: https://github.com/JuliaLang/julia/issues/14759
[#14798]: https://github.com/JuliaLang/julia/issues/14798
[#15032]: https://github.com/JuliaLang/julia/issues/15032
[#15172]: https://github.com/JuliaLang/julia/issues/15172
[#15192]: https://github.com/JuliaLang/julia/issues/15192
[#15242]: https://github.com/JuliaLang/julia/issues/15242
[#15244]: https://github.com/JuliaLang/julia/issues/15244
[#15258]: https://github.com/JuliaLang/julia/issues/15258
[#15431]: https://github.com/JuliaLang/julia/issues/15431
[#15550]: https://github.com/JuliaLang/julia/issues/15550
[#15609]: https://github.com/JuliaLang/julia/issues/15609
[#15731]: https://github.com/JuliaLang/julia/issues/15731
[#15763]: https://github.com/JuliaLang/julia/issues/15763
[#16058]: https://github.com/JuliaLang/julia/issues/16058
[#16107]: https://github.com/JuliaLang/julia/issues/16107
[#16219]: https://github.com/JuliaLang/julia/issues/16219
[#16260]: https://github.com/JuliaLang/julia/issues/16260
[#16362]: https://github.com/JuliaLang/julia/issues/16362
[#16403]: https://github.com/JuliaLang/julia/issues/16403
[#16481]: https://github.com/JuliaLang/julia/issues/16481
[#16731]: https://github.com/JuliaLang/julia/issues/16731
[#16972]: https://github.com/JuliaLang/julia/issues/16972