Julia v1.4 Release Notes

New language features

Structs with all isbits and isbitsunion fields are now stored inline in arrays (#32448).
import now allows quoted symbols, e.g. import Base.:+ (#33158).
Function composition now supports multiple functions: ∘(f, g, h) = f ∘ g ∘ h

and splatting ∘(fs...) for composing an iterable collection of functions (#33568).

Calling show or repr on an undef/UndefInitializer() array initializer now shows valid Julia code (#33211).
Calling show or repr on a 0-dimensional AbstractArray now shows valid code for creating an equivalent 0-dimensional array, instead of only showing the contained value. (#33206)

Windows build installer has switched to Inno Setup. Installer command line parameters have thus changed. For example, to extract the installer to a specific directory, the command line parameter is now /DIR=x:\dirname. Use julia-installer.exe /? to list all new command line parameters.

The splitpath function now accepts any AbstractString whereas previously it only accepted paths of type String (#33012).
The tempname function now takes an optional parent::AbstractString argument to give it a directory in which to attempt to produce a temporary path name (#33090).
The tempname function now takes a cleanup::Bool keyword argument defaulting to true, which causes the process to try to ensure that any file or directory at the path returned by tempname is deleted upon process exit (#33090).
The readdir function now takes a join::Bool keyword argument defaulting to false, which when set causes readdir to join its directory argument with each listed name (#33113).
readdir output is now guaranteed to be sorted. The sort keyword allows opting out of sorting to get names in OS-native order (#33542).
The new only(x) function returns the one-and-only element of a collection x, and throws an ArgumentError if x contains zero or multiple elements. (#33129)
takewhile and dropwhile have been added to the Iterators submodule (#33437).

The methods of mktemp and mktempdir which take a function body to pass temporary paths to no longer throw errors if the path is already deleted when the function body returns (#33091).
div now accepts a rounding mode as the third argument, consistent with the corresponding argument to rem. Support for rounding division, by passing one of the RoundNearest modes to this function, was added. For future compatibility, library authors should now extend this function, rather than extending the two-argument fld/cld/div directly. (#33040)
Verbose display of Char (text/plain output) now shows the codepoint value in standard-conforming "U+XXXX" format (#33291).
Iterators.partition now uses views (or smartly re-computed ranges) for partitions of all AbstractArrays (#33533).
Sets are now displayed less compactly in the REPL, as a column of elements, like vectors and dictionaries (#33300).

qr and qr! functions support blocksize keyword argument (#33053).
dot now admits a 3-argument method dot(x, A, y) to compute generalized dot products dot(x, A*y), but without computing and storing the intermediate result A*y (#32739).
ldlt and non-pivoted lu now throw a new ZeroPivotException type (#33372).
cond(A, p) with p=1 or p=Inf now computes the exact condition number instead of an estimate (#33547).

AbstractRNGs now behave like scalars when used in broadcasting (#33213).
Products involving sparse arrays now allow more general sparse eltypes, such as StaticArrays (#33205)
The performance of rand(::Tuple) is improved in some cases (#32208). As a consequence, the stream of generated values produced for a given seed has changed.

The attributes of the implicit IOContext used by the REPL to display objects can be modified by the user (experimental feature) (#29249).