Compat.jl

Compatibility across Julia versions
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October 2014

Compat Package for Julia

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The Compat package is designed to ease interoperability between older and newer versions of the Julia language. In particular, in cases where it is impossible to write code that works with both the latest Julia master branch and older Julia versions, or impossible to write code that doesn't generate a deprecation warning in some Julia version, the Compat package provides a macro that lets you use the latest syntax in a backwards-compatible way.

This is primarily intended for use by other Julia packages, where it is important to maintain cross-version compatibility.

Usage

To use Compat in your Julia package, add a line Compat = "34da2185-b29b-5c13-b0c7-acf172513d20" in the [deps] section and a line Compat = "..." in the [compat]section to the Project.toml file in your package directory. The version in the latter should be the minimum version that supports all needed fatures (see list below), and (if applicable) any newer major versions verified to be compatible. Then, in your package, shortly after the module statement a line like this:

using Compat

and then as needed add

@compat ...compat syntax...

wherever you want to use syntax that differs in the latest Julia master (the development version of Julia). The compat syntax is usually the syntax on Julia master. However, in a few cases where this is not possible, a slightly different syntax might be used. Please check the list below for the specific syntax you need.

Supported features

  • @inferred [AllowedType] f(x) is defined (#27516). (since Compat 3.12.0)

  • Search a character in a string with findfirst, findnext, findlast and findprev (#31664). (since Compat 3.12.0)

  • ∘(f) = f is defined (#34251). (since Compat 3.11.0)

  • union supports Base.OneTo (#35577). (since Compat 3.11.0)

  • get supports CartesianIndex when indexing AbstractArrays (#30268). (since Compat 3.10.0)

  • similar(::PermutedDimsArray) now uses the parent (#35304). (since Compat 3.9.0)

  • isdisjoint(l, r) indicates whether two collections are disjoint (#34427). (since Compat 3.9.0)

  • mergewith(combine, dicts...) and mergewith!(combine, dicts...) are like merge(combine, dicts...) and merge!(combine, dicts...) but without the restriction that the argument combine must be a Function (#34296). (since Compat 3.9.0).

  • @NamedTuple macro for convenient struct-like syntax for declaring NamedTuple types via key::Type declarations (#34548). (since Compat 3.8.0)

  • evalpoly(x, (p1, p2, ...)), the function equivalent to @evalpoly(x, p1, p2, ...) (#32753). (since Compat 3.7.0)

  • zero(::Irrational) and one now defined (#34773). (since Compat 3.6.0)

  • I1:I2, when I1 and I2 are CartesianIndex values, constructs a CartesianIndices iterator (#29440). (Since Compat 3.5.0)

  • oneunit(::CartesianIndex) replaces one(::CartesianIndex) (#29442). (Since Compat 3.5.0)

  • ismutable return true iff value v is mutable (#34652). (since Compat 3.4.0)

  • uuid5 generates a version 5 universally unique identifier (UUID), as specified by RFC 4122 (#28761). (since Compat 3.3.0)

  • dot now has a 3-argument method dot(x, A, y) without storing the intermediate result A*y (#32739). (since Compat 3.2.0)

  • pkgdir(m) returns the root directory of the package that imported module m (#33128). (since Compat 3.2.0)

  • filter can now act on a Tuple #32968. (since Compat 3.1.0)

  • Base.Order.ReverseOrdering has a zero arg constructor #33736. (since Compat 3.0.0)

  • Function composition now supports multiple functions: ∘(f, g, h) = f ∘ g ∘ h and splatting ∘(fs...) for composing an iterable collection of functions (#33568). (since Compat 3.0.0)

  • only(x) returns the one-and-only element of a collection x (#33129). (since Compat 2.2.0)

  • mod now accepts a unit range as the second argument (#32628). (since Compat 2.2.0)

  • eachrow, eachcol, and eachslice to iterate over first, second, or given dimension of an array (#29749). (since Compat 2.2.0)

  • isnothing for testing if a variable is equal to nothing (#29674). (since Compat 2.1.0)

  • hasproperty and hasfield (#28850). (since Compat 2.0.0)

  • merge methods with one and n NamedTuples (#29259). (since Compat 2.0.0)

  • range supporting stop as positional argument (#28708). (since Compat 1.3.0)

Developer tips

One of the most important rules for Compat.jl is to avoid breaking user code whenever possible, especially on a released version.

Although the syntax used in the most recent Julia version is the preferred compat syntax, there are cases where this shouldn't be used. Examples include when the new syntax already has a different meaning on previous versions of Julia, or when functions are removed from Base Julia and the alternative cannot be easily implemented on previous versions. In such cases, possible solutions are forcing the new feature to be used with qualified name in Compat.jl (e.g. use Compat.<name>) or reimplementing the old features on a later Julia version.

If you're adding additional compatibility code to this package, the contrib/commit-name.sh script in the base Julia repository is useful for extracting the version number from a git commit SHA. For example, from the git repository of julia, run something like this:

bash $ contrib/commit-name.sh a378b60fe483130d0d30206deb8ba662e93944da
0.5.0-dev+2023

This prints a version number corresponding to the specified commit of the form X.Y.Z-aaa+NNNN, and you can then test whether Julia is at least this version by VERSION >= v"X.Y.Z-aaa+NNNN".

Tagging the correct minimum version of Compat

Note that you should specify the correct minimum version for Compat in the [compat] section of your Project.toml, as given in above list.

Required Packages

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