You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
980 lines
34 KiB
980 lines
34 KiB
<!--{
|
|
"Title": "Go 1.2 Release Notes",
|
|
"Path": "/doc/go1.2",
|
|
"Template": true
|
|
}-->
|
|
|
|
<h2 id="introduction">Introduction to Go 1.2</h2>
|
|
|
|
<p>
|
|
Since the release of <a href="/doc/go1.1.html">Go version 1.1</a> in April, 2013,
|
|
the release schedule has been shortened to make the release process more efficient.
|
|
This release, Go version 1.2 or Go 1.2 for short, arrives roughly six months after 1.1,
|
|
while 1.1 took over a year to appear after 1.0.
|
|
Because of the shorter time scale, 1.2 is a smaller delta than the step from 1.0 to 1.1,
|
|
but it still has some significant developments, including
|
|
a better scheduler and one new language feature.
|
|
Of course, Go 1.2 keeps the <a href="/doc/go1compat.html">promise
|
|
of compatibility</a>.
|
|
The overwhelming majority of programs built with Go 1.1 (or 1.0 for that matter)
|
|
will run without any changes whatsoever when moved to 1.2,
|
|
although the introduction of one restriction
|
|
to a corner of the language may expose already-incorrect code
|
|
(see the discussion of the <a href="#use_of_nil">use of nil</a>).
|
|
</p>
|
|
|
|
<h2 id="language">Changes to the language</h2>
|
|
|
|
<p>
|
|
In the interest of firming up the specification, one corner case has been clarified,
|
|
with consequences for programs.
|
|
There is also one new language feature.
|
|
</p>
|
|
|
|
<h3 id="use_of_nil">Use of nil</h3>
|
|
|
|
<p>
|
|
The language now specifies that, for safety reasons,
|
|
certain uses of nil pointers are guaranteed to trigger a run-time panic.
|
|
For instance, in Go 1.0, given code like
|
|
</p>
|
|
|
|
<pre>
|
|
type T struct {
|
|
X [1<<24]byte
|
|
Field int32
|
|
}
|
|
|
|
func main() {
|
|
var x *T
|
|
...
|
|
}
|
|
</pre>
|
|
|
|
<p>
|
|
the <code>nil</code> pointer <code>x</code> could be used to access memory incorrectly:
|
|
the expression <code>x.Field</code> could access memory at address <code>1<<24</code>.
|
|
To prevent such unsafe behavior, in Go 1.2 the compilers now guarantee that any indirection through
|
|
a nil pointer, such as illustrated here but also in nil pointers to arrays, nil interface values,
|
|
nil slices, and so on, will either panic or return a correct, safe non-nil value.
|
|
In short, any expression that explicitly or implicitly requires evaluation of a nil address is an error.
|
|
The implementation may inject extra tests into the compiled program to enforce this behavior.
|
|
</p>
|
|
|
|
<p>
|
|
Further details are in the
|
|
<a href="//golang.org/s/go12nil">design document</a>.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>:
|
|
Most code that depended on the old behavior is erroneous and will fail when run.
|
|
Such programs will need to be updated by hand.
|
|
</p>
|
|
|
|
<h3 id="three_index">Three-index slices</h3>
|
|
|
|
<p>
|
|
Go 1.2 adds the ability to specify the capacity as well as the length when using a slicing operation
|
|
on an existing array or slice.
|
|
A slicing operation creates a new slice by describing a contiguous section of an already-created array or slice:
|
|
</p>
|
|
|
|
<pre>
|
|
var array [10]int
|
|
slice := array[2:4]
|
|
</pre>
|
|
|
|
<p>
|
|
The capacity of the slice is the maximum number of elements that the slice may hold, even after reslicing;
|
|
it reflects the size of the underlying array.
|
|
In this example, the capacity of the <code>slice</code> variable is 8.
|
|
</p>
|
|
|
|
<p>
|
|
Go 1.2 adds new syntax to allow a slicing operation to specify the capacity as well as the length.
|
|
A second
|
|
colon introduces the capacity value, which must be less than or equal to the capacity of the
|
|
source slice or array, adjusted for the origin. For instance,
|
|
</p>
|
|
|
|
<pre>
|
|
slice = array[2:4:7]
|
|
</pre>
|
|
|
|
<p>
|
|
sets the slice to have the same length as in the earlier example but its capacity is now only 5 elements (7-2).
|
|
It is impossible to use this new slice value to access the last three elements of the original array.
|
|
</p>
|
|
|
|
<p>
|
|
In this three-index notation, a missing first index (<code>[:i:j]</code>) defaults to zero but the other
|
|
two indices must always be specified explicitly.
|
|
It is possible that future releases of Go may introduce default values for these indices.
|
|
</p>
|
|
|
|
<p>
|
|
Further details are in the
|
|
<a href="//golang.org/s/go12slice">design document</a>.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>:
|
|
This is a backwards-compatible change that affects no existing programs.
|
|
</p>
|
|
|
|
<h2 id="impl">Changes to the implementations and tools</h2>
|
|
|
|
<h3 id="preemption">Pre-emption in the scheduler</h3>
|
|
|
|
<p>
|
|
In prior releases, a goroutine that was looping forever could starve out other
|
|
goroutines on the same thread, a serious problem when GOMAXPROCS
|
|
provided only one user thread.
|
|
In Go 1.2, this is partially addressed: The scheduler is invoked occasionally
|
|
upon entry to a function.
|
|
This means that any loop that includes a (non-inlined) function call can
|
|
be pre-empted, allowing other goroutines to run on the same thread.
|
|
</p>
|
|
|
|
<h3 id="thread_limit">Limit on the number of threads</h3>
|
|
|
|
<p>
|
|
Go 1.2 introduces a configurable limit (default 10,000) to the total number of threads
|
|
a single program may have in its address space, to avoid resource starvation
|
|
issues in some environments.
|
|
Note that goroutines are multiplexed onto threads so this limit does not directly
|
|
limit the number of goroutines, only the number that may be simultaneously blocked
|
|
in a system call.
|
|
In practice, the limit is hard to reach.
|
|
</p>
|
|
|
|
<p>
|
|
The new <a href="/pkg/runtime/debug/#SetMaxThreads"><code>SetMaxThreads</code></a> function in the
|
|
<a href="/pkg/runtime/debug/"><code>runtime/debug</code></a> package controls the thread count limit.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>:
|
|
Few functions will be affected by the limit, but if a program dies because it hits the
|
|
limit, it could be modified to call <code>SetMaxThreads</code> to set a higher count.
|
|
Even better would be to refactor the program to need fewer threads, reducing consumption
|
|
of kernel resources.
|
|
</p>
|
|
|
|
<h3 id="stack_size">Stack size</h3>
|
|
|
|
<p>
|
|
In Go 1.2, the minimum size of the stack when a goroutine is created has been lifted from 4KB to 8KB.
|
|
Many programs were suffering performance problems with the old size, which had a tendency
|
|
to introduce expensive stack-segment switching in performance-critical sections.
|
|
The new number was determined by empirical testing.
|
|
</p>
|
|
|
|
<p>
|
|
At the other end, the new function <a href="/pkg/runtime/debug/#SetMaxStack"><code>SetMaxStack</code></a>
|
|
in the <a href="/pkg/runtime/debug"><code>runtime/debug</code></a> package controls
|
|
the <em>maximum</em> size of a single goroutine's stack.
|
|
The default is 1GB on 64-bit systems and 250MB on 32-bit systems.
|
|
Before Go 1.2, it was too easy for a runaway recursion to consume all the memory on a machine.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>:
|
|
The increased minimum stack size may cause programs with many goroutines to use
|
|
more memory. There is no workaround, but plans for future releases
|
|
include new stack management technology that should address the problem better.
|
|
</p>
|
|
|
|
<h3 id="cgo_and_cpp">Cgo and C++</h3>
|
|
|
|
<p>
|
|
The <a href="/cmd/cgo/"><code>cgo</code></a> command will now invoke the C++
|
|
compiler to build any pieces of the linked-to library that are written in C++;
|
|
<a href="/cmd/cgo/">the documentation</a> has more detail.
|
|
</p>
|
|
|
|
<h3 id="go_tools_godoc">Godoc and vet moved to the go.tools subrepository</h3>
|
|
|
|
<p>
|
|
Both binaries are still included with the distribution, but the source code for the
|
|
godoc and vet commands has moved to the
|
|
<a href="//code.google.com/p/go.tools">go.tools</a> subrepository.
|
|
</p>
|
|
|
|
<p>
|
|
Also, the core of the godoc program has been split into a
|
|
<a href="https://code.google.com/p/go/source/browse/?repo=tools#hg%2Fgodoc">library</a>,
|
|
while the command itself is in a separate
|
|
<a href="https://code.google.com/p/go/source/browse/?repo=tools#hg%2Fcmd%2Fgodoc">directory</a>.
|
|
The move allows the code to be updated easily and the separation into a library and command
|
|
makes it easier to construct custom binaries for local sites and different deployment methods.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>:
|
|
Since godoc and vet are not part of the library,
|
|
no client Go code depends on the their source and no updating is required.
|
|
</p>
|
|
|
|
<p>
|
|
The binary distributions available from <a href="//golang.org">golang.org</a>
|
|
include these binaries, so users of these distributions are unaffected.
|
|
</p>
|
|
|
|
<p>
|
|
When building from source, users must use "go get" to install godoc and vet.
|
|
(The binaries will continue to be installed in their usual locations, not
|
|
<code>$GOPATH/bin</code>.)
|
|
</p>
|
|
|
|
<pre>
|
|
$ go get code.google.com/p/go.tools/cmd/godoc
|
|
$ go get code.google.com/p/go.tools/cmd/vet
|
|
</pre>
|
|
|
|
<h3 id="gccgo">Status of gccgo</h3>
|
|
|
|
<p>
|
|
We expect the future GCC 4.9 release to include gccgo with full
|
|
support for Go 1.2.
|
|
In the current (4.8.2) release of GCC, gccgo implements Go 1.1.2.
|
|
</p>
|
|
|
|
<h3 id="gc_changes">Changes to the gc compiler and linker</h3>
|
|
|
|
<p>
|
|
Go 1.2 has several semantic changes to the workings of the gc compiler suite.
|
|
Most users will be unaffected by them.
|
|
</p>
|
|
|
|
<p>
|
|
The <a href="/cmd/cgo/"><code>cgo</code></a> command now
|
|
works when C++ is included in the library being linked against.
|
|
See the <a href="/cmd/cgo/"><code>cgo</code></a> documentation
|
|
for details.
|
|
</p>
|
|
|
|
<p>
|
|
The gc compiler displayed a vestigial detail of its origins when
|
|
a program had no <code>package</code> clause: it assumed
|
|
the file was in package <code>main</code>.
|
|
The past has been erased, and a missing <code>package</code> clause
|
|
is now an error.
|
|
</p>
|
|
|
|
<p>
|
|
On the ARM, the toolchain supports "external linking", which
|
|
is a step towards being able to build shared libraries with the gc
|
|
toolchain and to provide dynamic linking support for environments
|
|
in which that is necessary.
|
|
</p>
|
|
|
|
<p>
|
|
In the runtime for the ARM, with <code>5a</code>, it used to be possible to refer
|
|
to the runtime-internal <code>m</code> (machine) and <code>g</code>
|
|
(goroutine) variables using <code>R9</code> and <code>R10</code> directly.
|
|
It is now necessary to refer to them by their proper names.
|
|
</p>
|
|
|
|
<p>
|
|
Also on the ARM, the <code>5l</code> linker (sic) now defines the
|
|
<code>MOVBS</code> and <code>MOVHS</code> instructions
|
|
as synonyms of <code>MOVB</code> and <code>MOVH</code>,
|
|
to make clearer the separation between signed and unsigned
|
|
sub-word moves; the unsigned versions already existed with a
|
|
<code>U</code> suffix.
|
|
</p>
|
|
|
|
<h3 id="cover">Test coverage</h3>
|
|
|
|
<p>
|
|
One major new feature of <a href="/pkg/go/"><code>go test</code></a> is
|
|
that it can now compute and, with help from a new, separately installed
|
|
"go tool cover" program, display test coverage results.
|
|
</p>
|
|
|
|
<p>
|
|
The cover tool is part of the
|
|
<a href="https://code.google.com/p/go/source/checkout?repo=tools"><code>go.tools</code></a>
|
|
subrepository.
|
|
It can be installed by running
|
|
</p>
|
|
|
|
<pre>
|
|
$ go get code.google.com/p/go.tools/cmd/cover
|
|
</pre>
|
|
|
|
<p>
|
|
The cover tool does two things.
|
|
First, when "go test" is given the <code>-cover</code> flag, it is run automatically
|
|
to rewrite the source for the package and insert instrumentation statements.
|
|
The test is then compiled and run as usual, and basic coverage statistics are reported:
|
|
</p>
|
|
|
|
<pre>
|
|
$ go test -cover fmt
|
|
ok fmt 0.060s coverage: 91.4% of statements
|
|
$
|
|
</pre>
|
|
|
|
<p>
|
|
Second, for more detailed reports, different flags to "go test" can create a coverage profile file,
|
|
which the cover program, invoked with "go tool cover", can then analyze.
|
|
</p>
|
|
|
|
<p>
|
|
Details on how to generate and analyze coverage statistics can be found by running the commands
|
|
</p>
|
|
|
|
<pre>
|
|
$ go help testflag
|
|
$ go tool cover -help
|
|
</pre>
|
|
|
|
<h3 id="go_doc">The go doc command is deleted</h3>
|
|
|
|
<p>
|
|
The "go doc" command is deleted.
|
|
Note that the <a href="/cmd/godoc/"><code>godoc</code></a> tool itself is not deleted,
|
|
just the wrapping of it by the <a href="/cmd/go/"><code>go</code></a> command.
|
|
All it did was show the documents for a package by package path,
|
|
which godoc itself already does with more flexibility.
|
|
It has therefore been deleted to reduce the number of documentation tools and,
|
|
as part of the restructuring of godoc, encourage better options in future.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>: For those who still need the precise functionality of running
|
|
</p>
|
|
|
|
<pre>
|
|
$ go doc
|
|
</pre>
|
|
|
|
<p>
|
|
in a directory, the behavior is identical to running
|
|
</p>
|
|
|
|
<pre>
|
|
$ godoc .
|
|
</pre>
|
|
|
|
<h3 id="gocmd">Changes to the go command</h3>
|
|
|
|
<p>
|
|
The <a href="/cmd/go/"><code>go get</code></a> command
|
|
now has a <code>-t</code> flag that causes it to download the dependencies
|
|
of the tests run by the package, not just those of the package itself.
|
|
By default, as before, dependencies of the tests are not downloaded.
|
|
</p>
|
|
|
|
<h2 id="performance">Performance</h2>
|
|
|
|
<p>
|
|
There are a number of significant performance improvements in the standard library; here are a few of them.
|
|
</p>
|
|
|
|
<ul>
|
|
|
|
<li>
|
|
The <a href="/pkg/compress/bzip2/"><code>compress/bzip2</code></a>
|
|
decompresses about 30% faster.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/crypto/des/"><code>crypto/des</code></a> package
|
|
is about five times faster.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/encoding/json/"><code>encoding/json</code></a> package
|
|
encodes about 30% faster.
|
|
</li>
|
|
|
|
<li>
|
|
Networking performance on Windows and BSD systems is about 30% faster through the use
|
|
of an integrated network poller in the runtime, similar to what was done for Linux and OS X
|
|
in Go 1.1.
|
|
</li>
|
|
|
|
</ul>
|
|
|
|
<h2 id="library">Changes to the standard library</h2>
|
|
|
|
|
|
<h3 id="archive_tar_zip">The archive/tar and archive/zip packages</h3>
|
|
|
|
<p>
|
|
The
|
|
<a href="/pkg/archive/tar/"><code>archive/tar</code></a>
|
|
and
|
|
<a href="/pkg/archive/zip/"><code>archive/zip</code></a>
|
|
packages have had a change to their semantics that may break existing programs.
|
|
The issue is that they both provided an implementation of the
|
|
<a href="/pkg/os/#FileInfo"><code>os.FileInfo</code></a>
|
|
interface that was not compliant with the specification for that interface.
|
|
In particular, their <code>Name</code> method returned the full
|
|
path name of the entry, but the interface specification requires that
|
|
the method return only the base name (final path element).
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>: Since this behavior was newly implemented and
|
|
a bit obscure, it is possible that no code depends on the broken behavior.
|
|
If there are programs that do depend on it, they will need to be identified
|
|
and fixed manually.
|
|
</p>
|
|
|
|
<h3 id="encoding">The new encoding package</h3>
|
|
|
|
<p>
|
|
There is a new package, <a href="/pkg/encoding/"><code>encoding</code></a>,
|
|
that defines a set of standard encoding interfaces that may be used to
|
|
build custom marshalers and unmarshalers for packages such as
|
|
<a href="/pkg/encoding/xml/"><code>encoding/xml</code></a>,
|
|
<a href="/pkg/encoding/json/"><code>encoding/json</code></a>,
|
|
and
|
|
<a href="/pkg/encoding/binary/"><code>encoding/binary</code></a>.
|
|
These new interfaces have been used to tidy up some implementations in
|
|
the standard library.
|
|
</p>
|
|
|
|
<p>
|
|
The new interfaces are called
|
|
<a href="/pkg/encoding/#BinaryMarshaler"><code>BinaryMarshaler</code></a>,
|
|
<a href="/pkg/encoding/#BinaryUnmarshaler"><code>BinaryUnmarshaler</code></a>,
|
|
<a href="/pkg/encoding/#TextMarshaler"><code>TextMarshaler</code></a>,
|
|
and
|
|
<a href="/pkg/encoding/#TextUnmarshaler"><code>TextUnmarshaler</code></a>.
|
|
Full details are in the <a href="/pkg/encoding/">documentation</a> for the package
|
|
and a separate <a href="//golang.org/s/go12encoding">design document</a>.
|
|
</p>
|
|
|
|
<h3 id="fmt_indexed_arguments">The fmt package</h3>
|
|
|
|
<p>
|
|
The <a href="/pkg/fmt/"><code>fmt</code></a> package's formatted print
|
|
routines such as <a href="/pkg/fmt/#Printf"><code>Printf</code></a>
|
|
now allow the data items to be printed to be accessed in arbitrary order
|
|
by using an indexing operation in the formatting specifications.
|
|
Wherever an argument is to be fetched from the argument list for formatting,
|
|
either as the value to be formatted or as a width or specification integer,
|
|
a new optional indexing notation <code>[</code><em>n</em><code>]</code>
|
|
fetches argument <em>n</em> instead.
|
|
The value of <em>n</em> is 1-indexed.
|
|
After such an indexing operating, the next argument to be fetched by normal
|
|
processing will be <em>n</em>+1.
|
|
</p>
|
|
|
|
<p>
|
|
For example, the normal <code>Printf</code> call
|
|
</p>
|
|
|
|
<pre>
|
|
fmt.Sprintf("%c %c %c\n", 'a', 'b', 'c')
|
|
</pre>
|
|
|
|
<p>
|
|
would create the string <code>"a b c"</code>, but with indexing operations like this,
|
|
</p>
|
|
|
|
<pre>
|
|
fmt.Sprintf("%[3]c %[1]c %c\n", 'a', 'b', 'c')
|
|
</pre>
|
|
|
|
<p>
|
|
the result is "<code>"c a b"</code>. The <code>[3]</code> index accesses the third formatting
|
|
argument, which is <code>'c'</code>, <code>[1]</code> accesses the first, <code>'a'</code>,
|
|
and then the next fetch accesses the argument following that one, <code>'b'</code>.
|
|
</p>
|
|
|
|
<p>
|
|
The motivation for this feature is programmable format statements to access
|
|
the arguments in different order for localization, but it has other uses:
|
|
</p>
|
|
|
|
<pre>
|
|
log.Printf("trace: value %v of type %[1]T\n", expensiveFunction(a.b[c]))
|
|
</pre>
|
|
|
|
<p>
|
|
<em>Updating</em>: The change to the syntax of format specifications
|
|
is strictly backwards compatible, so it affects no working programs.
|
|
</p>
|
|
|
|
<h3 id="text_template">The text/template and html/template packages</h3>
|
|
|
|
<p>
|
|
The
|
|
<a href="/pkg/text/template/"><code>text/template</code></a> package
|
|
has a couple of changes in Go 1.2, both of which are also mirrored in the
|
|
<a href="/pkg/html/template/"><code>html/template</code></a> package.
|
|
</p>
|
|
|
|
<p>
|
|
First, there are new default functions for comparing basic types.
|
|
The functions are listed in this table, which shows their names and
|
|
the associated familiar comparison operator.
|
|
</p>
|
|
|
|
<table cellpadding="0" summary="Template comparison functions">
|
|
<tr>
|
|
<th width="50"></th><th width="100">Name</th> <th width="50">Operator</th>
|
|
</tr>
|
|
<tr>
|
|
<td></td><td><code>eq</code></td> <td><code>==</code></td>
|
|
</tr>
|
|
<tr>
|
|
<td></td><td><code>ne</code></td> <td><code>!=</code></td>
|
|
</tr>
|
|
<tr>
|
|
<td></td><td><code>lt</code></td> <td><code><</code></td>
|
|
</tr>
|
|
<tr>
|
|
<td></td><td><code>le</code></td> <td><code><=</code></td>
|
|
</tr>
|
|
<tr>
|
|
<td></td><td><code>gt</code></td> <td><code>></code></td>
|
|
</tr>
|
|
<tr>
|
|
<td></td><td><code>ge</code></td> <td><code>>=</code></td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>
|
|
These functions behave slightly differently from the corresponding Go operators.
|
|
First, they operate only on basic types (<code>bool</code>, <code>int</code>,
|
|
<code>float64</code>, <code>string</code>, etc.).
|
|
(Go allows comparison of arrays and structs as well, under some circumstances.)
|
|
Second, values can be compared as long as they are the same sort of value:
|
|
any signed integer value can be compared to any other signed integer value for example. (Go
|
|
does not permit comparing an <code>int8</code> and an <code>int16</code>).
|
|
Finally, the <code>eq</code> function (only) allows comparison of the first
|
|
argument with one or more following arguments. The template in this example,
|
|
</p>
|
|
|
|
<pre>
|
|
{{"{{"}}if eq .A 1 2 3 {{"}}"}} equal {{"{{"}}else{{"}}"}} not equal {{"{{"}}end{{"}}"}}
|
|
</pre>
|
|
|
|
<p>
|
|
reports "equal" if <code>.A</code> is equal to <em>any</em> of 1, 2, or 3.
|
|
</p>
|
|
|
|
<p>
|
|
The second change is that a small addition to the grammar makes "if else if" chains easier to write.
|
|
Instead of writing,
|
|
</p>
|
|
|
|
<pre>
|
|
{{"{{"}}if eq .A 1{{"}}"}} X {{"{{"}}else{{"}}"}} {{"{{"}}if eq .A 2{{"}}"}} Y {{"{{"}}end{{"}}"}} {{"{{"}}end{{"}}"}}
|
|
</pre>
|
|
|
|
<p>
|
|
one can fold the second "if" into the "else" and have only one "end", like this:
|
|
</p>
|
|
|
|
<pre>
|
|
{{"{{"}}if eq .A 1{{"}}"}} X {{"{{"}}else if eq .A 2{{"}}"}} Y {{"{{"}}end{{"}}"}}
|
|
</pre>
|
|
|
|
<p>
|
|
The two forms are identical in effect; the difference is just in the syntax.
|
|
</p>
|
|
|
|
<p>
|
|
<em>Updating</em>: Neither the "else if" change nor the comparison functions
|
|
affect existing programs. Those that
|
|
already define functions called <code>eq</code> and so on through a function
|
|
map are unaffected because the associated function map will override the new
|
|
default function definitions.
|
|
</p>
|
|
|
|
<h3 id="new_packages">New packages</h3>
|
|
|
|
<p>
|
|
There are two new packages.
|
|
</p>
|
|
|
|
<ul>
|
|
<li>
|
|
The <a href="/pkg/encoding/"><code>encoding</code></a> package is
|
|
<a href="#encoding">described above</a>.
|
|
</li>
|
|
<li>
|
|
The <a href="/pkg/image/color/palette/"><code>image/color/palette</code></a> package
|
|
provides standard color palettes.
|
|
</li>
|
|
</ul>
|
|
|
|
<h3 id="minor_library_changes">Minor changes to the library</h3>
|
|
|
|
<p>
|
|
The following list summarizes a number of minor changes to the library, mostly additions.
|
|
See the relevant package documentation for more information about each change.
|
|
</p>
|
|
|
|
<ul>
|
|
|
|
<li>
|
|
The <a href="/pkg/archive/zip/"><code>archive/zip</code></a> package
|
|
adds the
|
|
<a href="/pkg/archive/zip/#File.DataOffset"><code>DataOffset</code></a> accessor
|
|
to return the offset of a file's (possibly compressed) data within the archive.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/bufio/"><code>bufio</code></a> package
|
|
adds <a href="/pkg/bufio/#Reader.Reset"><code>Reset</code></a>
|
|
methods to <a href="/pkg/bufio/#Reader"><code>Reader</code></a> and
|
|
<a href="/pkg/bufio/#Writer"><code>Writer</code></a>.
|
|
These methods allow the <a href="/pkg/io/#Reader"><code>Readers</code></a>
|
|
and <a href="/pkg/io/#Writer"><code>Writers</code></a>
|
|
to be re-used on new input and output readers and writers, saving
|
|
allocation overhead.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/compress/bzip2/"><code>compress/bzip2</code></a>
|
|
can now decompress concatenated archives.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/compress/flate/"><code>compress/flate</code></a>
|
|
package adds a <a href="/pkg/compress/flate/#Writer.Reset"><code>Reset</code></a>
|
|
method on the <a href="/pkg/compress/flate/#Writer"><code>Writer</code></a>,
|
|
to make it possible to reduce allocation when, for instance, constructing an
|
|
archive to hold multiple compressed files.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/compress/gzip/"><code>compress/gzip</code></a> package's
|
|
<a href="/pkg/compress/gzip/#Writer"><code>Writer</code></a> type adds a
|
|
<a href="/pkg/compress/gzip/#Writer.Reset"><code>Reset</code></a>
|
|
so it may be reused.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/compress/zlib/"><code>compress/zlib</code></a> package's
|
|
<a href="/pkg/compress/zlib/#Writer"><code>Writer</code></a> type adds a
|
|
<a href="/pkg/compress/zlib/#Writer.Reset"><code>Reset</code></a>
|
|
so it may be reused.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/container/heap/"><code>container/heap</code></a> package
|
|
adds a <a href="/pkg/container/heap/#Fix"><code>Fix</code></a>
|
|
method to provide a more efficient way to update an item's position in the heap.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/container/list/"><code>container/list</code></a> package
|
|
adds the <a href="/pkg/container/list/#List.MoveBefore"><code>MoveBefore</code></a>
|
|
and
|
|
<a href="/pkg/container/list/#List.MoveAfter"><code>MoveAfter</code></a>
|
|
methods, which implement the obvious rearrangement.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/crypto/cipher/"><code>crypto/cipher</code></a> package
|
|
adds the a new GCM mode (Galois Counter Mode), which is almost always
|
|
used with AES encryption.
|
|
</li>
|
|
|
|
<li>
|
|
The
|
|
<a href="/pkg/crypto/md5/"><code>crypto/md5</code></a> package
|
|
adds a new <a href="/pkg/crypto/md5/#Sum"><code>Sum</code></a> function
|
|
to simplify hashing without sacrificing performance.
|
|
</li>
|
|
|
|
<li>
|
|
Similarly, the
|
|
<a href="/pkg/crypto/md5/"><code>crypto/sha1</code></a> package
|
|
adds a new <a href="/pkg/crypto/sha1/#Sum"><code>Sum</code></a> function.
|
|
</li>
|
|
|
|
<li>
|
|
Also, the
|
|
<a href="/pkg/crypto/sha256/"><code>crypto/sha256</code></a> package
|
|
adds <a href="/pkg/crypto/sha256/#Sum256"><code>Sum256</code></a>
|
|
and <a href="/pkg/crypto/sha256/#Sum224"><code>Sum224</code></a> functions.
|
|
</li>
|
|
|
|
<li>
|
|
Finally, the <a href="/pkg/crypto/sha512/"><code>crypto/sha512</code></a> package
|
|
adds <a href="/pkg/crypto/sha512/#Sum512"><code>Sum512</code></a> and
|
|
<a href="/pkg/crypto/sha512/#Sum384"><code>Sum384</code></a> functions.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/crypto/x509/"><code>crypto/x509</code></a> package
|
|
adds support for reading and writing arbitrary extensions.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/crypto/tls/"><code>crypto/tls</code></a> package adds
|
|
support for TLS 1.1, 1.2 and AES-GCM.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/database/sql/"><code>database/sql</code></a> package adds a
|
|
<a href="/pkg/database/sql/#DB.SetMaxOpenConns"><code>SetMaxOpenConns</code></a>
|
|
method on <a href="/pkg/database/sql/#DB"><code>DB</code></a> to limit the
|
|
number of open connections to the database.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/encoding/csv/"><code>encoding/csv</code></a> package
|
|
now always allows trailing commas on fields.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/encoding/gob/"><code>encoding/gob</code></a> package
|
|
now treats channel and function fields of structures as if they were unexported,
|
|
even if they are not. That is, it ignores them completely. Previously they would
|
|
trigger an error, which could cause unexpected compatibility problems if an
|
|
embedded structure added such a field.
|
|
The package also now supports the generic <code>BinaryMarshaler</code> and
|
|
<code>BinaryUnmarshaler</code> interfaces of the
|
|
<a href="/pkg/encoding/"><code>encoding</code></a> package
|
|
described above.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/encoding/json/"><code>encoding/json</code></a> package
|
|
now will always escape ampersands as "\u0026" when printing strings.
|
|
It will now accept but correct invalid UTF-8 in
|
|
<a href="/pkg/encoding/json/#Marshal"><code>Marshal</code></a>
|
|
(such input was previously rejected).
|
|
Finally, it now supports the generic encoding interfaces of the
|
|
<a href="/pkg/encoding/"><code>encoding</code></a> package
|
|
described above.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/encoding/xml/"><code>encoding/xml</code></a> package
|
|
now allows attributes stored in pointers to be marshaled.
|
|
It also supports the generic encoding interfaces of the
|
|
<a href="/pkg/encoding/"><code>encoding</code></a> package
|
|
described above through the new
|
|
<a href="/pkg/encoding/xml/#Marshaler"><code>Marshaler</code></a>,
|
|
<a href="/pkg/encoding/xml/#Unmarshaler"><code>Unmarshaler</code></a>,
|
|
and related
|
|
<a href="/pkg/encoding/xml/#MarshalerAttr"><code>MarshalerAttr</code></a> and
|
|
<a href="/pkg/encoding/xml/#UnmarshalerAttr"><code>UnmarshalerAttr</code></a>
|
|
interfaces.
|
|
The package also adds a
|
|
<a href="/pkg/encoding/xml/#Encoder.Flush"><code>Flush</code></a> method
|
|
to the
|
|
<a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a>
|
|
type for use by custom encoders. See the documentation for
|
|
<a href="/pkg/encoding/xml/#Encoder.EncodeToken"><code>EncodeToken</code></a>
|
|
to see how to use it.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/flag/"><code>flag</code></a> package now
|
|
has a <a href="/pkg/flag/#Getter"><code>Getter</code></a> interface
|
|
to allow the value of a flag to be retrieved. Due to the
|
|
Go 1 compatibility guidelines, this method cannot be added to the existing
|
|
<a href="/pkg/flag/#Value"><code>Value</code></a>
|
|
interface, but all the existing standard flag types implement it.
|
|
The package also now exports the <a href="/pkg/flag/#CommandLine"><code>CommandLine</code></a>
|
|
flag set, which holds the flags from the command line.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/go/ast/"><code>go/ast</code></a> package's
|
|
<a href="/pkg/go/ast/#SliceExpr"><code>SliceExpr</code></a> struct
|
|
has a new boolean field, <code>Slice3</code>, which is set to true
|
|
when representing a slice expression with three indices (two colons).
|
|
The default is false, representing the usual two-index form.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/go/build/"><code>go/build</code></a> package adds
|
|
the <code>AllTags</code> field
|
|
to the <a href="/pkg/go/build/#Package"><code>Package</code></a> type,
|
|
to make it easier to process build tags.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/image/draw/"><code>image/draw</code></a> package now
|
|
exports an interface, <a href="/pkg/image/draw/#Drawer"><code>Drawer</code></a>,
|
|
that wraps the standard <a href="/pkg/image/draw/#Draw"><code>Draw</code></a> method.
|
|
The Porter-Duff operators now implement this interface, in effect binding an operation to
|
|
the draw operator rather than providing it explicitly.
|
|
Given a paletted image as its destination, the new
|
|
<a href="/pkg/image/draw/#FloydSteinberg"><code>FloydSteinberg</code></a>
|
|
implementation of the
|
|
<a href="/pkg/image/draw/#Drawer"><code>Drawer</code></a>
|
|
interface will use the Floyd-Steinberg error diffusion algorithm to draw the image.
|
|
To create palettes suitable for such processing, the new
|
|
<a href="/pkg/image/draw/#Quantizer"><code>Quantizer</code></a> interface
|
|
represents implementations of quantization algorithms that choose a palette
|
|
given a full-color image.
|
|
There are no implementations of this interface in the library.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/image/gif/"><code>image/gif</code></a> package
|
|
can now create GIF files using the new
|
|
<a href="/pkg/image/gif/#Encode"><code>Encode</code></a>
|
|
and <a href="/pkg/image/gif/#EncodeAll"><code>EncodeAll</code></a>
|
|
functions.
|
|
Their options argument allows specification of an image
|
|
<a href="/pkg/image/draw/#Quantizer"><code>Quantizer</code></a> to use;
|
|
if it is <code>nil</code>, the generated GIF will use the
|
|
<a href="/pkg/image/color/palette/#Plan9"><code>Plan9</code></a>
|
|
color map (palette) defined in the new
|
|
<a href="/pkg/image/color/palette/"><code>image/color/palette</code></a> package.
|
|
The options also specify a
|
|
<a href="/pkg/image/draw/#Drawer"><code>Drawer</code></a>
|
|
to use to create the output image;
|
|
if it is <code>nil</code>, Floyd-Steinberg error diffusion is used.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/io/#Copy"><code>Copy</code></a> method of the
|
|
<a href="/pkg/io/"><code>io</code></a> package now prioritizes its
|
|
arguments differently.
|
|
If one argument implements <a href="/pkg/io/#WriterTo"><code>WriterTo</code></a>
|
|
and the other implements <a href="/pkg/io/#ReaderFrom"><code>ReaderFrom</code></a>,
|
|
<a href="/pkg/io/#Copy"><code>Copy</code></a> will now invoke
|
|
<a href="/pkg/io/#WriterTo"><code>WriterTo</code></a> to do the work,
|
|
so that less intermediate buffering is required in general.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/"><code>net</code></a> package requires cgo by default
|
|
because the host operating system must in general mediate network call setup.
|
|
On some systems, though, it is possible to use the network without cgo, and useful
|
|
to do so, for instance to avoid dynamic linking.
|
|
The new build tag <code>netgo</code> (off by default) allows the construction of a
|
|
<code>net</code> package in pure Go on those systems where it is possible.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/"><code>net</code></a> package adds a new field
|
|
<code>DualStack</code> to the <a href="/pkg/net/#Dialer"><code>Dialer</code></a>
|
|
struct for TCP connection setup using a dual IP stack as described in
|
|
<a href="https://tools.ietf.org/html/rfc6555">RFC 6555</a>.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/net/http/"><code>net/http</code></a> package will no longer
|
|
transmit cookies that are incorrect according to
|
|
<a href="https://tools.ietf.org/html/rfc6265">RFC 6265</a>.
|
|
It just logs an error and sends nothing.
|
|
Also,
|
|
the <a href="/pkg/net/http/"><code>net/http</code></a> package's
|
|
<a href="/pkg/net/http/#ReadResponse"><code>ReadResponse</code></a>
|
|
function now permits the <code>*Request</code> parameter to be <code>nil</code>,
|
|
whereupon it assumes a GET request.
|
|
Finally, an HTTP server will now serve HEAD
|
|
requests transparently, without the need for special casing in handler code.
|
|
While serving a HEAD request, writes to a
|
|
<a href="/pkg/net/http/#Handler"><code>Handler</code></a>'s
|
|
<a href="/pkg/net/http/#ResponseWriter"><code>ResponseWriter</code></a>
|
|
are absorbed by the
|
|
<a href="/pkg/net/http/#Server"><code>Server</code></a>
|
|
and the client receives an empty body as required by the HTTP specification.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/os/exec/"><code>os/exec</code></a> package's
|
|
<a href="/pkg/os/exec/#Cmd.StdinPipe"><code>Cmd.StdinPipe</code></a> method
|
|
returns an <code>io.WriteCloser</code>, but has changed its concrete
|
|
implementation from <code>*os.File</code> to an unexported type that embeds
|
|
<code>*os.File</code>, and it is now safe to close the returned value.
|
|
Before Go 1.2, there was an unavoidable race that this change fixes.
|
|
Code that needs access to the methods of <code>*os.File</code> can use an
|
|
interface type assertion, such as <code>wc.(interface{ Sync() error })</code>.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/runtime/"><code>runtime</code></a> package relaxes
|
|
the constraints on finalizer functions in
|
|
<a href="/pkg/runtime/#SetFinalizer"><code>SetFinalizer</code></a>: the
|
|
actual argument can now be any type that is assignable to the formal type of
|
|
the function, as is the case for any normal function call in Go.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/sort/"><code>sort</code></a> package has a new
|
|
<a href="/pkg/sort/#Stable"><code>Stable</code></a> function that implements
|
|
stable sorting. It is less efficient than the normal sort algorithm, however.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/strings/"><code>strings</code></a> package adds
|
|
an <a href="/pkg/strings/#IndexByte"><code>IndexByte</code></a>
|
|
function for consistency with the <a href="/pkg/bytes/"><code>bytes</code></a> package.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/sync/atomic/"><code>sync/atomic</code></a> package
|
|
adds a new set of swap functions that atomically exchange the argument with the
|
|
value stored in the pointer, returning the old value.
|
|
The functions are
|
|
<a href="/pkg/sync/atomic/#SwapInt32"><code>SwapInt32</code></a>,
|
|
<a href="/pkg/sync/atomic/#SwapInt64"><code>SwapInt64</code></a>,
|
|
<a href="/pkg/sync/atomic/#SwapUint32"><code>SwapUint32</code></a>,
|
|
<a href="/pkg/sync/atomic/#SwapUint64"><code>SwapUint64</code></a>,
|
|
<a href="/pkg/sync/atomic/#SwapUintptr"><code>SwapUintptr</code></a>,
|
|
and
|
|
<a href="/pkg/sync/atomic/#SwapPointer"><code>SwapPointer</code></a>,
|
|
which swaps an <code>unsafe.Pointer</code>.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/syscall/"><code>syscall</code></a> package now implements
|
|
<a href="/pkg/syscall/#Sendfile"><code>Sendfile</code></a> for Darwin.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/testing/"><code>testing</code></a> package
|
|
now exports the <a href="/pkg/testing/#TB"><code>TB</code></a> interface.
|
|
It records the methods in common with the
|
|
<a href="/pkg/testing/#T"><code>T</code></a>
|
|
and
|
|
<a href="/pkg/testing/#B"><code>B</code></a> types,
|
|
to make it easier to share code between tests and benchmarks.
|
|
Also, the
|
|
<a href="/pkg/testing/#AllocsPerRun"><code>AllocsPerRun</code></a>
|
|
function now quantizes the return value to an integer (although it
|
|
still has type <code>float64</code>), to round off any error caused by
|
|
initialization and make the result more repeatable.
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/text/template/"><code>text/template</code></a> package
|
|
now automatically dereferences pointer values when evaluating the arguments
|
|
to "escape" functions such as "html", to bring the behavior of such functions
|
|
in agreement with that of other printing functions such as "printf".
|
|
</li>
|
|
|
|
<li>
|
|
In the <a href="/pkg/time/"><code>time</code></a> package, the
|
|
<a href="/pkg/time/#Parse"><code>Parse</code></a> function
|
|
and
|
|
<a href="/pkg/time/#Time.Format"><code>Format</code></a>
|
|
method
|
|
now handle time zone offsets with seconds, such as in the historical
|
|
date "1871-01-01T05:33:02+00:34:08".
|
|
Also, pattern matching in the formats for those routines is stricter: a non-lowercase letter
|
|
must now follow the standard words such as "Jan" and "Mon".
|
|
</li>
|
|
|
|
<li>
|
|
The <a href="/pkg/unicode/"><code>unicode</code></a> package
|
|
adds <a href="/pkg/unicode/#In"><code>In</code></a>,
|
|
a nicer-to-use but equivalent version of the original
|
|
<a href="/pkg/unicode/#IsOneOf"><code>IsOneOf</code></a>,
|
|
to see whether a character is a member of a Unicode category.
|
|
</li>
|
|
|
|
</ul>
|