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- <!--{
- "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>
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