Go 1.18 is not yet released. These are work-in-progress release notes. Go 1.18 is expected to be released in February 2022.
TODO: complete this section
The Go 1.18 compiler now correctly reports declared but not used errors
for variables that are set inside a function literal but are never used. Before Go 1.18,
the compiler did not report an error in such cases. This fixes long-outstanding compiler
issue #8560. As a result of this change,
(possibly incorrect) programs may not compile anymore. The necessary fix is
straightforward: fix the program if it was in fact incorrect, or use the offending
variable, for instance by assigning it to the blank identifier _.
Since go vet always pointed out this error, the number of affected
programs is likely very small.
The Go 1.18 compiler now reports an overflow when passing a rune constant expression
such as '1' << 32 as an argument to the predeclared functions
print and println, consistent with the behavior of
user-defined functions. Before Go 1.18, the compiler did not report an error
in such cases but silently accepted such constant arguments if they fit into an
int64. As a result of this change, (possibly incorrect) programs
may not compile anymore. The necessary fix is straightforward: fix the program if it
was in fact incorrect, or explicitly convert the offending argument to the correct type.
Since go vet always pointed out this error, the number of affected
programs is likely very small.
Go 1.18 includes an implementation of generics as described by the generics proposal.
The current generics implementation has the following limitations:
Go 1.18 includes an implementation of fuzzing as described by the fuzzing proposal.
See the fuzzing landing page to get started.
Please be aware that fuzzing can consume a lot of memory and may impact your
machine’s performance while it runs. Also be aware that the fuzzing engine
writes values that expand test coverage to a fuzz cache directory within
$GOCACHE/fuzz while it runs. There is currently no limit to the
number of files or total bytes that may be written to the fuzz cache, so it
may occupy a large amount of storage (possibly several GBs).
Go 1.18 introduces the new GOAMD64 environment variable which selects
a version of the AMD64 architecture. Allowed values are v1,
v2, v3, or v4. Each higher level requires,
and takes advantage of, additional processor features. A detailed description of the
versions is here.
The GOAMD64 environment variable defaults to v1.
The 64-bit RISC-V architecture on Linux (the linux/riscv64 port)
now supports the c-archive and c-shared build modes.
The windows/arm and windows/arm64 ports now support
non-cooperative preemption, bringing that capability to all four Windows
ports, which should hopefully address subtle bugs encountered when calling
into Win32 functions that block for extended periods of time.
On iOS (the ios/arm64 port)
and iOS simulator running on AMD64-based macOS (the ios/amd64 port),
Go 1.18 now requires iOS 12 or later; support for previous versions has been discontinued.
Go 1.18 is the last release that is supported on FreeBSD 11.x, which has already reached end-of-life. Go 1.19 will require FreeBSD 12.2+ or FreeBSD 13.0+. FreeBSD 13.0+ will require a kernel with the COMPAT_FREEBSD12 option set (this is the default).
go get no longer builds or installs packages in
module-aware mode. go get is now dedicated to
adjusting dependencies in go.mod. Effectively, the
-d flag is always enabled. To install the latest version
of an executable outside the context of the current module, use
go
install example.com/cmd@latest. Any
version query
may be used instead of latest. This form of go
install was added in Go 1.16, so projects supporting older
versions may need to provide install instructions for both go
install and go get. go
get now reports an error when used outside a module, since there
is no go.mod file to update. In GOPATH mode (with
GO111MODULE=off), go get still builds
and installs packages, as before.
The go command now embeds version control information in
binaries including the currently checked-out revision, commit time, and a
flag indicating whether edited or untracked files are present. Version
control information is embedded if the go command is invoked in
a directory within a Git, Mercurial, Fossil, or Bazaar repository, and the
main package and its containing main module are in the same
repository. This information may be omitted using the flag
-buildvcs=false.
Additionally, the go command embeds information about the build
including build and tool tags (set with -tags), compiler,
assembler, and linker flags (like -gcflags), whether cgo was
enabled, and if it was, the values of the cgo environment variables
(like CGO_CFLAGS). This information may be omitted using the
flag -buildinfo=false. Both VCS and build information may be
read together with module information using go
version -m file or
runtime/debug.ReadBuildInfo (for the currently running binary)
or the new debug/buildinfo
package.
If the main module's go.mod file
specifies go 1.17
or higher, go mod download without
arguments now downloads source code for only the modules
explicitly required in the main
module's go.mod file. (In a go 1.17 or
higher module, that set already includes all dependencies needed to build the
packages and tests in the main module.)
To also download source code for transitive dependencies, use
go mod download all.
The go mod vendor subcommand now
supports a -o flag to set the output directory.
(Other go commands still read from the vendor
directory at the module root when loading packages
with -mod=vendor, so the main use for this flag is for
third-party tools that need to collect package source code.)
The go build command and related commands
now support an -asan flag that enables interoperation
with C (or C++) code compiled with the address sanitizer (C compiler
option -fsanitize=address).
gofmt
gofmt now reads and formats input files concurrently, with a
memory limit proportional to GOMAXPROCS. On a machine with
multiple CPUs, gofmt should now be significantly faster.
The garbage collector now includes non-heap sources of garbage collector work
(e.g., stack scanning) when determining how frequently to run. As a result,
garbage collector overhead is more predictable when these sources are
significant. For most applications these changes will be negligible; however,
some Go applications may now use less memory and spend more time on garbage
collection, or vice versa, than before. The intended workaround is to tweak
GOGC where necessary.
The runtime now returns memory to the operating system more efficiently and has been tuned to work more aggressively as a result.
Go 1.17 generally improved the formatting of arguments in stack traces,
but could print inaccurate values for arguments passed in registers.
This is improved in Go 1.18 by printing a question mark (?)
after each value that may be inaccurate.
Go 1.17 implemented a new way of passing
function arguments and results using registers instead of the stack
on 64-bit x86 architecture on selected operating systems.
Go 1.18 expands the supported platforms to include 64-bit ARM (GOARCH=arm64),
big- and little-endian 64-bit PowerPC (GOARCH=ppc64, ppc64le),
as well as 64-bit x86 architecture (GOARCH=amd64)
on all operating systems.
On 64-bit ARM and 64-bit PowerPC systems, benchmarking shows
typical performance improvements of 10% or more.
As mentioned in the Go 1.17 release notes, this change does not affect the functionality of any safe Go code and is designed to have no impact on most assembly code. See the Go 1.17 release notes for more details.
The compiler now can inline functions that contain range loops or labeled for loops.
The new compiler -asan option supports the
new go command -asan option.
TODO: Mention build speed impact.
The new linker -asan option supports the
new go command -asan option.
constraints package
The new constraints package
defines a set of useful constraints that can be used with type parameters of
generic functions.
net/netip package
The new net/netip
package defines a new IP address type, Addr.
Compared to the existing
net.IP type, the netip.Addr type takes less
memory, is immutable, and is comparable so it supports ==
and can be used as a map key.
In addition to Addr, the package defines
AddrPort, representing
an IP and port, and
Prefix, representing
a network CIDR prefix.
The net package now has methods to send and receive UDP packets
using netip.Addr values instead of the relatively heavy
*net.UDPAddr values.
TODO: complete this section
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind.
TODO: complete this section
The new Writer.AvailableBuffer
method returns an empty buffer with a possibly non-empty capacity for use
with append-like APIs. After appending, the buffer can be provided to a
succeeding Write call and possibly avoid any copying.
The methods Reader.Reset and
Writer.Reset
now use the default buffer size when called on objects with a
nil buffer.
Trim, TrimLeft,
and TrimRight are now allocation free and, especially for
small ASCII cutsets, up to 10 times faster.
The Title function is now deprecated. It doesn't
handle Unicode punctuation and language-specific capitalization rules, and is superseded by the
golang.org/x/text/cases package.
TODO: bytes.Cut.
The new Conn.NetConn
method allows access to the underlying
net.Conn.
This new package provides access to module versions, version control
information, and build flags embedded in executable files built by
the go command. The same information is also available via
runtime/debug.ReadBuildInfo
for the currently running binary and via go
version -m on the command line.
The new Kind.String
method returns a human-readable name for the receiver kind.
The new constant TILDE
represents the ~ token per the proposal
Additions to go/ast and go/token to support parameterized functions and types
.
The Draw and DrawMask fallback implementations
(used when the arguments are not the most common image types) are now
faster when those arguments implement the optional
draw.RGBA64Image
and image.RGBA64Image
interfaces that were added in Go 1.17.
net.Error.Temporary has been deprecated.
TODO: Several new net APIs.
On WebAssembly targets, the Dial, DialContext,
DialTLS and DialTLSContext method fields in
Transport
will now be correctly used, if specified, for making HTTP requests.
The new
Cookie.Valid
method reports whether the cookie is valid.
User.GroupIds.
now uses a Go native implementation when cgo is not available.
The new
Value.SetIterKey
and Value.SetIterValue
methods set a Value using a map iterator as the source. They are equivalent to
Value.Set(iter.Key()) and Value.Set(iter.Value()) but
do fewer allocations.
The new
Value.UnsafePointer
method returns the Value's value as an unsafe.Pointer.
This allows callers to migrate from Value.UnsafeAddr
and Value.Pointer
to eliminate the need to perform uintptr to unsafe.Pointer conversions at the callsite (as unsafe.Pointer rules require).
The new
MapIter.Reset
method changes its receiver to iterate over a
different map. The use of
MapIter.Reset
allows allocation-free iteration
over many maps.
A number of methods (
Value.CanInt,
Value.CanUint,
Value.CanFloat,
Value.CanComplex
)
have been added to
Value
to test if a conversion is safe.
Value.FieldByIndexErr
has been added to avoid the panic that occurs in
Value.FieldByIndex
when stepping through a nil pointer to an embedded struct.
reflect.Ptr and
reflect.PtrTo
have been renamed to
reflect.Pointer and
reflect.PointerTo,
respectively, for consistency with the rest of the reflect package.
The old names will continue to work, but will be deprecated in a
future Go release.
TODO: https://golang.org/cl/354569: document and implement that invalid UTF-8 bytes are the same as U+FFFD
TODO: https://golang.org/cl/343877: reject surrogate halves in Unquote
The new Clone function copies the input
string without the returned cloned string referencing
the input string's memory.
Trim, TrimLeft,
and TrimRight are now allocation free and, especially for
small ASCII cutsets, up to 10 times faster.
The Title function is now deprecated. It doesn't
handle Unicode punctuation and language-specific capitalization rules, and is superseded by the
golang.org/x/text/cases package.
TODO: strings.Cut.
TODO: https://golang.org/cl/319769: add Mutex.TryLock, RWMutex.TryLock, RWMutex.TryRLock
The new function SyscallN
has been introduced for Windows, allowing for calls with arbitrary number
of arguments. As a result,
Syscall,
Syscall6,
Syscall9,
Syscall12,
Syscall15, and
Syscall18 are
deprecated in favor of SyscallN.
TODO: https://golang.org/cl/355570: add support for SysProcAttr.Pdeathsig on FreeBSD
TODO: https://golang.org/cl/356430: remove Wrapper interface
TODO: https://golang.org/cl/343883: increase alternation precedence
TODO: https://golang.org/cl/356669: skip extra -count iterations if there are no tests
The and function no longer always evaluates all arguments; it
stops evaluating arguments after the first argument that evaluates to
false. Similarly, the or function now stops evaluating
arguments after the first argument that evaluates to true. This makes a
difference if any of the arguments is a function call.
The AppendRune function appends the UTF-8 new
encoding of a rune to a []byte.