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.
Go 1.18 includes an implementation of generic features as described by the Type Parameters Proposal. This includes major - but fully backward-compatible - changes to the language.
These new language changes required a large amount of new code that has not had significant testing in production settings. That will only happen as more people write and use generic code. We believe that this feature is well implemented and high quality. However, unlike most aspects of Go, we can't back up that belief with real world experience. Therefore, while we encourage the use of generics where it makes sense, please use appropriate caution when deploying generic code in production.
The following is a list of the most visible changes. For a more comprehensive overview, see the proposal. For details see the language spec.
~ has been added to the set of
operators and punctuation.
~T type elements. Such interfaces may only be used
as type constraints.
An interface now defines a set of types as well as a set of methods.
any is an alias for the empty interface. It may be used instead of
interface{}.
comparable is an interface that denotes the set of all types which can be
compared using == or !=. It may only be used as (or embedded in)
a type constraint.
There are three experimental packages using generics that may be useful. These packages are in x/exp repository; their API is not covered by the Go 1 guarantee and may change as we gain more experience with generics.
golang.org/x/exp/constraints
Constraints that are useful for generic code, such as
constraints.Ordered.
golang.org/x/exp/slicesA collection of generic functions that operate on slices of any element type.
golang.org/x/exp/mapsA collection of generic functions that operate on maps of any key or element type.
The current generics implementation has the following limitations:
real, imag, and complex.
We hope to remove this restriction in Go 1.19.
m on a value
x of type parameter type P if m is explicitly
declared by P's constraint interface.
Similarly, method values x.m and method expressions
P.m also are only supported if m is explicitly
declared by P, even though m might be in the method set
of P by virtue of the fact that all types in P implement
m. We hope to remove this restriction in Go 1.19.
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 introduces the new GOAMD64 environment variable, which selects at compile time
a minimum target 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 can be found
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.
Go 1.18 requires Linux kernel version 2.6.32 or later.
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 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 get
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.
go.mod and go.sum updates
The go mod graph,
go mod vendor,
go mod verify, and
go mod why subcommands
no longer automatically update the go.mod and
go.sum files.
(Those files can be updated explicitly using go get,
go mod tidy, or
go mod download.)
go version
The go command now embeds version control information in
binaries. It includes 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).
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.
The underlying data format of the embedded build information can change with
new go releases, so an older version of go may not handle the
build information produced with a newer version of go.
To read the version information from a binary built with go 1.18,
use the go version command and the
debug/buildinfo package from go 1.18+.
go mod download
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.
go mod vendor
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.)
go mod tidy
The go mod tidy command now retains
additional checksums in the go.sum file for modules whose source
code is needed to verify that each imported package is provided by only one
module in the build list. Because this
condition is rare and failure to apply it results in a build error, this
change is not conditioned on the go version in the main
module's go.mod file.
go work
The go command now supports a "Workspace" mode. If a
go.work file is found in the working directory or a
parent directory, or one is specified using the GOWORK
environment variable, it will put the go command into workspace mode.
In workspace mode, the go.work file will be used to
determine the set of main modules used as the roots for module
resolution, instead of using the normally-found go.mod
file to specify the single main module. For more information see the
go work
documentation.
go build -asan
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).
go test
The go command now supports additional command line
options for the new fuzzing support described
above:
go test supports
-fuzz, -fuzztime, and
-fuzzminimizetime options.
For documentation on these see
go help testflag.
go clean supports a -fuzzcache
option.
For documentation see
go help clean.
//go:build lines
Go 1.17 introduced //go:build lines as a more readable way to write build constraints,
instead of // +build lines.
As of Go 1.17, gofmt adds //go:build lines
to match existing +build lines and keeps them in sync,
while go vet diagnoses when they are out of sync.
Since the release of Go 1.18 marks the end of support for Go 1.16,
all supported versions of Go now understand //go:build lines.
In Go 1.18, go fix now removes the now-obsolete
// +build lines in modules declaring
go 1.17 or later in their go.mod files.
For more information, see https://go.dev/design/draft-gobuild.
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 vet tool is updated to support generic code. In most cases,
it reports an error in generic code whenever it would report an error in the
equivalent non-generic code after substituting for type parameters with a
type from their
type set.
For example, vet reports a format error in
func Print[T ~int|~string](t T) {
fmt.Printf("%d", t)
}
because it would report a format error in the non-generic equivalent of
Print[string]:
func PrintString(x string) {
fmt.Printf("%d", x)
}
The cmd/vet checkers copylock, printf,
sortslice, testinggoroutine, and tests
have all had moderate precision improvements to handle additional code patterns.
This may lead to newly reported errors in existing packages. For example, the
printf checker now tracks formatting strings created by
concatenating string constants. So vet will report an error in:
// fmt.Printf formatting directive %d is being passed to Println.
fmt.Println("%d"+` ≡ x (mod 2)`+"\n", x%2)
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 -asan compiler option supports the
new go command -asan option.
Because the compiler's type checker was replaced in its entirety to support generics, some error messages now may use different wording than before. In some cases, pre-Go 1.18 error messages provided more detail or were phrased in a more helpful way. We intend to address these cases in Go 1.19.
Because of changes in the compiler related to supporting generics, the Go 1.18 compile speed can be roughly 15% slower than the Go 1.17 compile speed. The execution time of the compiled code is not affected. We intend to improve the speed of the compiler in Go 1.19.
The linker emits far fewer relocations.
As a result, most codebases will link faster, require less memory to link,
and generate smaller binaries.
Tools that process Go binaries should use Go 1.18's debug/gosym package
to transparently handle both old and new binaries.
The new -asan linker option supports the
new go command -asan option.
When building a Go release from source and GOROOT_BOOTSTRAP
is not set, previous versions of Go looked for a Go 1.4 or later bootstrap toolchain
in the directory $HOME/go1.4 (%HOMEDRIVE%%HOMEPATH%\go1.4 on Windows).
Go now looks first for $HOME/go1.17 or $HOME/sdk/go1.17
before falling back to $HOME/go1.4.
We intend for Go 1.19 to require Go 1.17 or later for bootstrap,
and this change should make the transition smoother.
For more details, see go.dev/issue/44505.
debug/buildinfo package
The new debug/buildinfo 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.
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 package also defines several functions to create and examine
these new types:
AddrFrom4,
AddrFrom16,
AddrFromSlice,
AddrPortFrom,
IPv4Unspecified,
IPv6LinkLocalAllNodes,
IPv6Unspecified,
MustParseAddr,
MustParseAddrPort,
MustParsePrefix,
ParseAddr,
ParseAddrPort,
ParsePrefix,
PrefixFrom.
The net package includes new
methods that parallel existing methods, but
return netip.AddrPort instead of the
heavier-weight net.IP or
*net.UDPAddr types:
Resolver.LookupNetIP,
UDPConn.ReadFromUDPAddrPort,
UDPConn.ReadMsgUDPAddrPort,
UDPConn.WriteToUDPAddrPort,
UDPConn.WriteMsgUDPAddrPort.
The new UDPConn methods support allocation-free I/O.
The net package also now includes functions and methods
to convert between the existing
TCPAddr/UDPAddr
types and netip.AddrPort:
TCPAddrFromAddrPort,
UDPAddrFromAddrPort,
TCPAddr.AddrPort,
UDPAddr.AddrPort.
If Config.MinVersion
is not set, it now defaults to TLS 1.2 for client connections. Any safely
up-to-date server is expected to support TLS 1.2, and browsers have required
it since 2020. TLS 1.0 and 1.1 are still supported by setting
Config.MinVersion to VersionTLS10.
The server-side default is unchanged at TLS 1.0.
The default can be temporarily reverted to TLS 1.0 by setting the
GODEBUG=tls10default=1 environment variable.
This option will be removed in Go 1.19.
crypto/x509 will now
reject certificates signed with the SHA-1 hash function. This doesn't
apply to self-signed root certificates. Practical attacks against SHA-1
have been demonstrated since 2017 and publicly
trusted Certificate Authorities have not issued SHA-1 certificates since 2015.
This can be temporarily reverted by setting the
GODEBUG=x509sha1=1 environment variable.
This option will be removed in Go 1.19.
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind.
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 Reader.Reset and
Writer.Reset methods
now use the default buffer size when called on objects with a
nil buffer.
The new Cut function
slices a []byte around a separator. It can replace
and simplify many common uses of
Index,
IndexByte,
IndexRune,
and SplitN.
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.
The P224,
P384, and
P521 curve
implementations are now all backed by code generated by the
addchain and
fiat-crypto
projects, the latter of which is based on a formally-verified model
of the arithmetic operations. They now use safer complete formulas
and internal APIs. P-224 and P-384 are now approximately four times
faster. All specific curve implementations are now constant-time.
Operating on invalid curve points (those for which the
IsOnCurve method returns false, and which are never returned
by Unmarshal or
a Curve method operating on a valid point) has always been
undefined behavior, can lead to key recovery attacks, and is now
unsupported by the new backend. If an invalid point is supplied to a
P224, P384, or P521 method, that
method will now return a random point. The behavior might change to an
explicit panic in a future release.
The new Conn.NetConn
method allows access to the underlying
net.Conn.
Certificate.Verify
now uses platform APIs to verify certificate validity on macOS and iOS when it
is called with a nil
VerifyOpts.Roots
or when using the root pool returned from
SystemCertPool.
SystemCertPool
is now available on Windows.
On Windows, macOS, and iOS, when a
CertPool returned by
SystemCertPool
has additional certificates added to it,
Certificate.Verify
will do two verifications: one using the platform verifier APIs and the
system roots, and one using the Go verifier and the additional roots.
Chains returned by the platform verifier APIs will be prioritized.
CertPool.Subjects
is deprecated. On Windows, macOS, and iOS the
CertPool returned by
SystemCertPool
will return a pool which does not include system roots in the slice
returned by Subjects, as a static list can't appropriately
represent the platform policies and might not be available at all from the
platform APIs.
The StructField
and BasicType
structs both now have a DataBitOffset field, which
holds the value of the DW_AT_data_bit_offset
attribute if present.
The R_PPC64_RELATIVE
constant has been added.
The File.Symbols method now returns the new exported error value ErrNoSymbols if the file has no symbol section.
Per the proposal
Additions to go/ast and go/token to support parameterized functions and types
the following additions are made to the go/ast package:
FuncType
and TypeSpec
nodes have a new field TypeParams to hold type parameters, if any.
IndexListExpr
represents index expressions with multiple indices, used for function and type instantiations
with more than one explicit type argument.
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 new Config.GoVersion
field sets the accepted Go language version.
Per the proposal
Additions to go/types to support type parameters
the following additions are made to the go/types package:
TypeParam, factory function
NewTypeParam,
and associated methods are added to represent a type parameter.
TypeParamList holds a list of
type parameters.
TypeList holds a list of types.
NewSignatureType allocates a
Signature with
(receiver or function) type parameters.
To access those type parameters, the Signature type has two new methods
Signature.RecvTypeParams and
Signature.TypeParams.
Named types have four new methods:
Named.Origin to get the original
parameterized types of instantiated types,
Named.TypeArgs and
Named.TypeParams to get the
type arguments or type parameters of an instantiated or parameterized type, and
Named.SetTypeParams to set the
type parameters (for instance, when importing a named type where allocation of the named
type and setting of type parameters cannot be done simultaneously due to possible cycles).
Interface type has four new methods:
Interface.IsComparable and
Interface.IsMethodSet to
query properties of the type set defined by the interface, and
Interface.MarkImplicit and
Interface.IsImplicit to set
and test whether the interface is an implicit interface around a type constraint literal.
Union and
Term, factory functions
NewUnion and
NewTerm, and associated
methods are added to represent type sets in interfaces.
Instantiate
instantiates a parameterized type.
Info.Instances
map records function and type instantiations through the new
Instance type.
ArgumentError
and associated methods are added to represent an error related to a type argument.
Context and factory function
NewContext
are added to facilitate sharing of identical type instances
across type-checked packages, via the new
Config.Context
field.
The predicates
AssignableTo,
ConvertibleTo,
Implements,
Identical,
IdenticalIgnoreTags, and
AssertableTo
now also work with arguments that are or contain generalized interfaces, i.e. interfaces
that may only be used as type constraints in Go code.
Note that the behavior of AssertableTo is undefined if the first argument
is a generalized interface.
Within a range pipeline the new
{{break}} command will end the loop early and the
new {{continue}} command will immediately start the
next loop iteration.
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 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.
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.
The new
MaxBytesHandler
function creates a Handler that wraps its
ResponseWriter and Request.Body with a
MaxBytesReader.
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.
regexp
now treats each invalid byte of a UTF-8 string as U+FFFD.
The BuildInfo
struct has two new fields, containing additional information
about how the binary was built:
GoVersion
holds the version of Go used to build the binary.
Settings
is a slice of
BuildSettings
structs holding key/value pairs describing the build.
The CPU profiler now uses per-thread timers on Linux. This increases the maximum CPU usage that a profile can observe, and reduces some forms of bias.
strconv.Unquote
now rejects Unicode surrogate halves.
The new Cut function
slices a string around a separator. It can replace
and simplify many common uses of
Index,
IndexByte,
IndexRune,
and SplitN.
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.
The new methods
Mutex.TryLock,
RWMutex.TryLock, and
RWMutex.TryRLock,
will acquire the lock if it is not currently held.
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.
SysProcAttr.Pdeathsig
is now supported in FreeBSD.
The Wrapper interface has been removed.
The precedence of / in the argument for -run and
-bench has been increased. A/B|C/D used to be
treated as A/(B|C)/D and is now treated as
(A/B)|(C/D).
If the -run option does not select any tests, the
-count option is ignored. This could change the behavior of
existing tests in the unlikely case that a test changes the set of subtests
that are run each time the test function itself is run.
The new testing.F type
is used by the new fuzzing support described
above. Tests also now support the command line
options -test.fuzz, -test.fuzztime, and
-test.fuzzminimizetime.
Within a range pipeline the new
{{break}} command will end the loop early and the
new {{continue}} command will immediately start the
next loop iteration.
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 package supports the new
text/template and
html/template
{{break}} command via the new constant
NodeBreak
and the new type
BreakNode,
and similarly supports the new {{continue}} command
via the new constant
NodeContinue
and the new type
ContinueNode.
The new AppendRune function appends the UTF-8
encoding of a rune to a []byte.