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.
To use Compat in your Julia package, add it as a dependency of your package using the package manager
pkg> add Compat
and add a version specifier line
such as Compat = "3.22, 4"
in the [compat]
section of the Project.toml
file
in your package directory. The version in the latter should be the minimum
version that supports all needed features (see list below). Note that Compat v4
requires Julia v1.6, but some features may have been backported to Compat v3
(see the
feature list of the release-3 branch).
If you require any of those backported features, be sure to specify the correct
compatibility in your Project.toml
. E.g. if the feature from Compat v4.x has
been backported to v3.y, use Compat = 3.y, 4.x
. If you use a feature that had
originally been added in Compat v3 (e.g. in 3.x), don't forget to also declare
compatibility with v4 with Compat = 3.x, 4
(unless you use one the very few
things that got removed between Compat v3 and v4,
which you most probably don't).
To minimize dependency conflicts between packages it is recommended that packages allow for both appropriate v4 and v3 versions of Compat.jl in their Project.toml (except for rare cases of packages that support only v4 or v3 version of Compat.jl).
Then, in your package, shortly after the module
statement include 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.
Features in the development versions of julia
may be added and released in
Compat.jl. However, such features are considered experimental until the
relevant julia
version is released. These features can be changed or removed
without incrementing the major version of Compat.jl if necessary to match
changes in julia
.
-
redirect_stdio
, for simple stream redirection. (#37978) (since Compat 4.8.0) -
trunc
,floor
,ceil
, andround
toBool
. (#25085) (since Compat 4.7.0) -
splat(f)
which is equivalent toargs -> f(args...)
. (#42717, #48038) (since Compat 4.6.0) (Note: for historical reasons,Compat
on Julia before v1.9 also exportsSplat
; its usage is discouraged, however.) -
Compat.@assume_effects setting... ex
overrides the compiler's effect modeling for the method definitionex
on Julia versions that support this feature. Julia version without support just pass backex
. (#43852) (since Compat 4.4.0) -
div
,lcm
,gcd
,/
,rem
, andmod
willpromote
heterogenousDates.Period
s (@bdf9ead9
). (since Compat 4.3.0) -
stack
combines a collection of slices into one array (#43334). (since Compat 4.2.0) -
keepat!
removes the items at all the indices which are not given and returns the modified source (#36229, #42351). (since Compat 4.1.0) -
@compat (; a, b) = (; c=1, b=2, a=3)
supports property descturing assignment syntax (#39285). -
allequal
, the opposite ofallunique
(#43354). (since Compat 3.42.0) -
eachsplit
for iteratively performing split(str). (#39245). (since Compat 3.41.0) -
ismutabletype(t::Type)
check whether a type is mutable (the fieldmutable
ofDataType
was removed. #39037) (since Compat 3.40) -
convert(::Type{<:Period}, ::CompoundPeriod)
can convertCompoundPeriod
s into the specifiedPeriod
type (#40803) (since Compat 3.38.0) -
Compat.@inline
andCompat.@noinline
can be used at function callsites to encourage the compiler to (not) inline the function calls on Julia versions that support these features, and otherwise do not have any effects (#41312) (since Compat 3.37) -
Compat.@inline
andCompat.@noinline
can be used within function body to hint to the compiler the inlineability of the defined function (#41312) (since Compat 3.37) -
Compat.@constprop :aggressive ex
andCompat.@constprop :none ex
allow control over constant-propagation during inference on Julia versions that support this feature, and otherwise just pass backex
. (#42125) (since Compat 3.36) -
Returns(value)
returnsvalue
for any arguments (#39794) (since Compat 3.35) -
The function
current_exceptions()
has been added to get the current exception stack. Julia-1.0 lacks runtime support for full execption stacks, so we return only the most recent exception in that case. (#29901) (since Compat 3.34) -
Two argument methods
findmax(f, domain)
,argmax(f, domain)
and the correspondingmin
versions (#35316, #41076) (since Compat 3.31.1) -
isunordered(x)
returns true ifx
is value that is normally unordered, such asNaN
ormissing
(#35316) (since Compat 3.31.1) -
get
accepts tuples and numbers (#41007, #41032) (since Compat 3.31) -
@something
and@coalesce
as short-circuiting versions ofsomething
andcoalesce
(#40729) (since Compat 3.29)
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"
.
Note that you should specify the correct minimum version for Compat
in the
[compat]
section of your Project.toml
, as given in above list.