mirror of
https://github.com/golang/go
synced 2024-11-23 19:20:03 -07:00
docs: remove some prose-unworthy empty parentheses.
In our evolving style, prose should name a function "f" not "f()". R=gri, rsc CC=golang-dev https://golang.org/cl/4550075
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@ -935,13 +935,14 @@ example of its possibilities.
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<h2 id="data">Data</h2>
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<h3 id="allocation_new">Allocation with <code>new()</code></h3>
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<h3 id="allocation_new">Allocation with <code>new</code></h3>
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<p>
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Go has two allocation primitives, <code>new()</code> and <code>make()</code>.
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Go has two allocation primitives, the built-in functions
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<code>new</code> and <code>make</code>.
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They do different things and apply to different types, which can be confusing,
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but the rules are simple.
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Let's talk about <code>new()</code> first.
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Let's talk about <code>new</code> first.
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It's a built-in function essentially the same as its namesakes
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in other languages: <code>new(T)</code> allocates zeroed storage for a new item of type
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<code>T</code> and returns its address, a value of type <code>*T</code>.
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@ -950,9 +951,9 @@ In Go terminology, it returns a pointer to a newly allocated zero value of type
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</p>
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<p>
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Since the memory returned by <code>new()</code> is zeroed, it's helpful to arrange that the
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Since the memory returned by <code>new</code> is zeroed, it's helpful to arrange that the
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zeroed object can be used without further initialization. This means a user of
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the data structure can create one with <code>new()</code> and get right to
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the data structure can create one with <code>new</code> and get right to
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work.
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For example, the documentation for <code>bytes.Buffer</code> states that
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"the zero value for <code>Buffer</code> is an empty buffer ready to use."
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@ -1065,7 +1066,7 @@ s := []string {Enone: "no error", Eio: "Eio", Einval: "invalid argument"}
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m := map[int]string{Enone: "no error", Eio: "Eio", Einval: "invalid argument"}
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</pre>
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<h3 id="allocation_make">Allocation with <code>make()</code></h3>
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<h3 id="allocation_make">Allocation with <code>make</code></h3>
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<p>
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Back to allocation.
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@ -1099,8 +1100,8 @@ In contrast, <code>new([]int)</code> returns a pointer to a newly allocated, zer
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structure, that is, a pointer to a <code>nil</code> slice value.
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<p>
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These examples illustrate the difference between <code>new()</code> and
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<code>make()</code>.
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These examples illustrate the difference between <code>new</code> and
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<code>make</code>.
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</p>
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<pre>
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@ -1116,9 +1117,9 @@ v := make([]int, 100)
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</pre>
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<p>
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Remember that <code>make()</code> applies only to maps, slices and channels
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Remember that <code>make</code> applies only to maps, slices and channels
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and does not return a pointer.
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To obtain an explicit pointer allocate with <code>new()</code>.
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To obtain an explicit pointer allocate with <code>new</code>.
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</p>
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<h3 id="arrays">Arrays</h3>
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@ -1473,7 +1474,7 @@ map[string] int
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</pre>
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<p>
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If you want to control the default format for a custom type, all that's required is to define
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a method <code>String() string</code> on the type.
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a method with the signature <code>String() string</code> on the type.
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For our simple type <code>T</code>, that might look like this.
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</p>
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<pre>
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@ -1495,7 +1496,7 @@ that's more efficient and idiomatic for struct types.
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See the section below on <a href="#pointers_vs_values">pointers vs. value receivers</a> for more information.)
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</p>
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<p>
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Our <code>String()</code> method is able to call <code>Sprintf</code> because the
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Our <code>String</code> method is able to call <code>Sprintf</code> because the
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print routines are fully reentrant and can be used recursively.
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We can even go one step further and pass a print routine's arguments directly to another such routine.
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The signature of <code>Printf</code> uses the type <code>...interface{}</code>
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@ -1683,19 +1684,20 @@ var (
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<h3 id="init">The init function</h3>
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<p>
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Finally, each source file can define its own <code>init()</code> function to
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set up whatever state is required. The only restriction is that, although
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Finally, each source file can define its own niladic <code>init</code> function to
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set up whatever state is required. (Actually each file can have multiple
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<code>init</code> functions.) The only restriction is that, although
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goroutines can be launched during initialization, they will not begin
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execution until it completes; initialization always runs as a single thread
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of execution.
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And finally means finally: <code>init()</code> is called after all the
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And finally means finally: <code>init</code> is called after all the
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variable declarations in the package have evaluated their initializers,
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and those are evaluated only after all the imported packages have been
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initialized.
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</p>
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<p>
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Besides initializations that cannot be expressed as declarations,
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a common use of <code>init()</code> functions is to verify or repair
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a common use of <code>init</code> functions is to verify or repair
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correctness of the program state before real execution begins.
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</p>
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@ -1899,7 +1901,7 @@ on every instance of a common method.
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In such cases, the constructor should return an interface value
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rather than the implementing type.
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As an example, in the hash libraries
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both <code>crc32.NewIEEE()</code> and <code>adler32.New()</code>
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both <code>crc32.NewIEEE</code> and <code>adler32.New</code>
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return the interface type <code>hash.Hash32</code>.
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Substituting the CRC-32 algorithm for Adler-32 in a Go program
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requires only changing the constructor call;
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@ -1,5 +1,5 @@
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<!-- title The Go Programming Language Specification -->
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<!-- subtitle Version of May 23, 2011 -->
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<!-- subtitle Version of May 24, 2011 -->
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<!--
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TODO
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@ -821,7 +821,7 @@ make([]T, length, capacity)
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</pre>
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<p>
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The <code>make()</code> call allocates a new, hidden array to which the returned
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A call to <code>make</code> allocates a new, hidden array to which the returned
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slice value refers. That is, executing
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</p>
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@ -4931,7 +4931,7 @@ func main() {
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<h3 id="The_zero_value">The zero value</h3>
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<p>
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When memory is allocated to store a value, either through a declaration
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or <code>make()</code> or <code>new()</code> call,
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or a call of <code>make</code> or <code>new</code>,
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and no explicit initialization is provided, the memory is
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given a default initialization. Each element of such a value is
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set to the <i>zero value</i> for its type: <code>false</code> for booleans,
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@ -4989,7 +4989,7 @@ func init()
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<p>
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defined in its source.
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A package may contain multiple
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<code>init()</code> functions, even
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<code>init</code> functions, even
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within a single source file; they execute
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in unspecified order.
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</p>
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@ -5019,8 +5019,8 @@ program is complete. Therefore, all initialization code is run in a single
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goroutine.
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</p>
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<p>
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An <code>init()</code> function cannot be referred to from anywhere
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in a program. In particular, <code>init()</code> cannot be called explicitly,
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An <code>init</code> function cannot be referred to from anywhere
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in a program. In particular, <code>init</code> cannot be called explicitly,
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nor can a pointer to <code>init</code> be assigned to a function variable.
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</p>
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<p>
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@ -341,7 +341,7 @@ Using slices one can write this function (from <code>sum.go</code>):
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15 }
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</pre>
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<p>
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Note how the return type (<code>int</code>) is defined for <code>sum()</code> by stating it
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Note how the return type (<code>int</code>) is defined for <code>sum</code> by stating it
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after the parameter list.
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<p>
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To call the function, we slice the array. This intricate call (we'll show
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@ -373,7 +373,7 @@ There are also maps, which you can initialize like this:
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m := map[string]int{"one":1 , "two":2}
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</pre>
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<p>
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The built-in function <code>len()</code>, which returns number of elements,
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The built-in function <code>len</code>, which returns number of elements,
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makes its first appearance in <code>sum</code>. It works on strings, arrays,
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slices, maps, and channels.
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<p>
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@ -401,7 +401,7 @@ for more examples of its use.
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Most types in Go are values. If you have an <code>int</code> or a <code>struct</code>
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or an array, assignment
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copies the contents of the object.
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To allocate a new variable, use <code>new()</code>, which
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To allocate a new variable, use the built-in function <code>new</code>, which
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returns a pointer to the allocated storage.
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<p>
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<pre>
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@ -418,7 +418,7 @@ or the more idiomatic
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Some types—maps, slices, and channels (see below)—have reference semantics.
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If you're holding a slice or a map and you modify its contents, other variables
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referencing the same underlying data will see the modification. For these three
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types you want to use the built-in function <code>make()</code>:
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types you want to use the built-in function <code>make</code>:
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<p>
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<pre>
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m := make(map[string]int)
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@ -432,11 +432,11 @@ If you just declare the map, as in
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</pre>
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<p>
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it creates a <code>nil</code> reference that cannot hold anything. To use the map,
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you must first initialize the reference using <code>make()</code> or by assignment from an
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you must first initialize the reference using <code>make</code> or by assignment from an
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existing map.
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<p>
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Note that <code>new(T)</code> returns type <code>*T</code> while <code>make(T)</code> returns type
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<code>T</code>. If you (mistakenly) allocate a reference object with <code>new()</code>,
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<code>T</code>. If you (mistakenly) allocate a reference object with <code>new</code> rather than <code>make</code>,
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you receive a pointer to a nil reference, equivalent to
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declaring an uninitialized variable and taking its address.
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<p>
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@ -767,7 +767,7 @@ Building on the <code>file</code> package, here's a simple version of the Unix u
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By now this should be easy to follow, but the <code>switch</code> statement introduces some
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new features. Like a <code>for</code> loop, an <code>if</code> or <code>switch</code> can include an
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initialization statement. The <code>switch</code> on line 18 uses one to create variables
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<code>nr</code> and <code>er</code> to hold the return values from <code>f.Read()</code>. (The <code>if</code> on line 25
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<code>nr</code> and <code>er</code> to hold the return values from the call to <code>f.Read</code>. (The <code>if</code> on line 25
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has the same idea.) The <code>switch</code> statement is general: it evaluates the cases
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from top to bottom looking for the first case that matches the value; the
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case expressions don't need to be constants or even integers, as long as
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@ -779,14 +779,14 @@ in a <code>for</code> statement, a missing value means <code>true</code>. In fa
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is a form of <code>if-else</code> chain. While we're here, it should be mentioned that in
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<code>switch</code> statements each <code>case</code> has an implicit <code>break</code>.
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<p>
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Line 25 calls <code>Write()</code> by slicing the incoming buffer, which is itself a slice.
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Line 25 calls <code>Write</code> by slicing the incoming buffer, which is itself a slice.
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Slices provide the standard Go way to handle I/O buffers.
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<p>
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Now let's make a variant of <code>cat</code> that optionally does <code>rot13</code> on its input.
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It's easy to do by just processing the bytes, but instead we will exploit
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Go's notion of an <i>interface</i>.
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<p>
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The <code>cat()</code> subroutine uses only two methods of <code>f</code>: <code>Read()</code> and <code>String()</code>,
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The <code>cat</code> subroutine uses only two methods of <code>f</code>: <code>Read</code> and <code>String</code>,
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so let's start by defining an interface that has exactly those two methods.
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Here is code from <code>progs/cat_rot13.go</code>:
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<p>
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@ -838,7 +838,7 @@ To use the new feature, we define a flag:
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14 var rot13Flag = flag.Bool("rot13", false, "rot13 the input")
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</pre>
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<p>
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and use it from within a mostly unchanged <code>cat()</code> function:
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and use it from within a mostly unchanged <code>cat</code> function:
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<p>
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<pre> <!-- progs/cat_rot13.go /func.cat/ /^}/ -->
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52 func cat(r reader) {
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@ -866,7 +866,7 @@ and use it from within a mostly unchanged <code>cat()</code> function:
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74 }
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</pre>
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<p>
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(We could also do the wrapping in <code>main</code> and leave <code>cat()</code> mostly alone, except
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(We could also do the wrapping in <code>main</code> and leave <code>cat</code> mostly alone, except
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for changing the type of the argument; consider that an exercise.)
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Lines 56 through 58 set it all up: If the <code>rot13</code> flag is true, wrap the <code>reader</code>
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we received into a <code>rotate13</code> and proceed. Note that the interface variables
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@ -1055,7 +1055,7 @@ to that of the <code>Printf</code> call above.
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</pre>
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<p>
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If you have your own type you'd like <code>Printf</code> or <code>Print</code> to format,
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just give it a <code>String()</code> method that returns a string. The print
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just give it a <code>String</code> method that returns a string. The print
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routines will examine the value to inquire whether it implements
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the method and if so, use it rather than some other formatting.
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Here's a simple example.
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@ -1076,14 +1076,14 @@ Here's a simple example.
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21 }
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</pre>
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<p>
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Since <code>*testType</code> has a <code>String()</code> method, the
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Since <code>*testType</code> has a <code>String</code> method, the
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default formatter for that type will use it and produce the output
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<p>
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<pre>
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77 Sunset Strip
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</pre>
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<p>
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Observe that the <code>String()</code> method calls <code>Sprint</code> (the obvious Go
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Observe that the <code>String</code> method calls <code>Sprint</code> (the obvious Go
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variant that returns a string) to do its formatting; special formatters
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can use the <code>fmt</code> library recursively.
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<p>
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@ -1096,7 +1096,7 @@ and such, but that's getting a little off the main thread so we'll leave it
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as an exploration exercise.
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<p>
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You might ask, though, how <code>Printf</code> can tell whether a type implements
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the <code>String()</code> method. Actually what it does is ask if the value can
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the <code>String</code> method. Actually what it does is ask if the value can
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be converted to an interface variable that implements the method.
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Schematically, given a value <code>v</code>, it does this:
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<p>
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@ -1141,7 +1141,7 @@ interface type defined in the <code>io</code> library:
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<p>
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(This interface is another conventional name, this time for <code>Write</code>; there are also
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<code>io.Reader</code>, <code>io.ReadWriter</code>, and so on.)
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Thus you can call <code>Fprintf</code> on any type that implements a standard <code>Write()</code>
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Thus you can call <code>Fprintf</code> on any type that implements a standard <code>Write</code>
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method, not just files but also network channels, buffers, whatever
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you want.
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<p>
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|
@ -272,7 +272,7 @@ Using slices one can write this function (from "sum.go"):
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|
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--PROG progs/sum.go /sum/ /^}/
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|
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Note how the return type ("int") is defined for "sum()" by stating it
|
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Note how the return type ("int") is defined for "sum" by stating it
|
||||
after the parameter list.
|
||||
|
||||
To call the function, we slice the array. This intricate call (we'll show
|
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@ -296,7 +296,7 @@ There are also maps, which you can initialize like this:
|
||||
|
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m := map[string]int{"one":1 , "two":2}
|
||||
|
||||
The built-in function "len()", which returns number of elements,
|
||||
The built-in function "len", which returns number of elements,
|
||||
makes its first appearance in "sum". It works on strings, arrays,
|
||||
slices, maps, and channels.
|
||||
|
||||
@ -321,7 +321,7 @@ An Interlude about Allocation
|
||||
Most types in Go are values. If you have an "int" or a "struct"
|
||||
or an array, assignment
|
||||
copies the contents of the object.
|
||||
To allocate a new variable, use "new()", which
|
||||
To allocate a new variable, use the built-in function "new", which
|
||||
returns a pointer to the allocated storage.
|
||||
|
||||
type T struct { a, b int }
|
||||
@ -334,7 +334,7 @@ or the more idiomatic
|
||||
Some types—maps, slices, and channels (see below)—have reference semantics.
|
||||
If you're holding a slice or a map and you modify its contents, other variables
|
||||
referencing the same underlying data will see the modification. For these three
|
||||
types you want to use the built-in function "make()":
|
||||
types you want to use the built-in function "make":
|
||||
|
||||
m := make(map[string]int)
|
||||
|
||||
@ -344,11 +344,11 @@ If you just declare the map, as in
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var m map[string]int
|
||||
|
||||
it creates a "nil" reference that cannot hold anything. To use the map,
|
||||
you must first initialize the reference using "make()" or by assignment from an
|
||||
you must first initialize the reference using "make" or by assignment from an
|
||||
existing map.
|
||||
|
||||
Note that "new(T)" returns type "*T" while "make(T)" returns type
|
||||
"T". If you (mistakenly) allocate a reference object with "new()",
|
||||
"T". If you (mistakenly) allocate a reference object with "new" rather than "make",
|
||||
you receive a pointer to a nil reference, equivalent to
|
||||
declaring an uninitialized variable and taking its address.
|
||||
|
||||
@ -526,7 +526,7 @@ Building on the "file" package, here's a simple version of the Unix utility "cat
|
||||
By now this should be easy to follow, but the "switch" statement introduces some
|
||||
new features. Like a "for" loop, an "if" or "switch" can include an
|
||||
initialization statement. The "switch" on line 18 uses one to create variables
|
||||
"nr" and "er" to hold the return values from "f.Read()". (The "if" on line 25
|
||||
"nr" and "er" to hold the return values from the call to "f.Read". (The "if" on line 25
|
||||
has the same idea.) The "switch" statement is general: it evaluates the cases
|
||||
from top to bottom looking for the first case that matches the value; the
|
||||
case expressions don't need to be constants or even integers, as long as
|
||||
@ -538,14 +538,14 @@ in a "for" statement, a missing value means "true". In fact, such a "switch"
|
||||
is a form of "if-else" chain. While we're here, it should be mentioned that in
|
||||
"switch" statements each "case" has an implicit "break".
|
||||
|
||||
Line 25 calls "Write()" by slicing the incoming buffer, which is itself a slice.
|
||||
Line 25 calls "Write" by slicing the incoming buffer, which is itself a slice.
|
||||
Slices provide the standard Go way to handle I/O buffers.
|
||||
|
||||
Now let's make a variant of "cat" that optionally does "rot13" on its input.
|
||||
It's easy to do by just processing the bytes, but instead we will exploit
|
||||
Go's notion of an <i>interface</i>.
|
||||
|
||||
The "cat()" subroutine uses only two methods of "f": "Read()" and "String()",
|
||||
The "cat" subroutine uses only two methods of "f": "Read" and "String",
|
||||
so let's start by defining an interface that has exactly those two methods.
|
||||
Here is code from "progs/cat_rot13.go":
|
||||
|
||||
@ -569,11 +569,11 @@ To use the new feature, we define a flag:
|
||||
|
||||
--PROG progs/cat_rot13.go /rot13Flag/
|
||||
|
||||
and use it from within a mostly unchanged "cat()" function:
|
||||
and use it from within a mostly unchanged "cat" function:
|
||||
|
||||
--PROG progs/cat_rot13.go /func.cat/ /^}/
|
||||
|
||||
(We could also do the wrapping in "main" and leave "cat()" mostly alone, except
|
||||
(We could also do the wrapping in "main" and leave "cat" mostly alone, except
|
||||
for changing the type of the argument; consider that an exercise.)
|
||||
Lines 56 through 58 set it all up: If the "rot13" flag is true, wrap the "reader"
|
||||
we received into a "rotate13" and proceed. Note that the interface variables
|
||||
@ -701,19 +701,19 @@ to that of the "Printf" call above.
|
||||
--PROG progs/print.go 'NR==21' 'NR==22'
|
||||
|
||||
If you have your own type you'd like "Printf" or "Print" to format,
|
||||
just give it a "String()" method that returns a string. The print
|
||||
just give it a "String" method that returns a string. The print
|
||||
routines will examine the value to inquire whether it implements
|
||||
the method and if so, use it rather than some other formatting.
|
||||
Here's a simple example.
|
||||
|
||||
--PROG progs/print_string.go 'NR==9' END
|
||||
|
||||
Since "*testType" has a "String()" method, the
|
||||
Since "*testType" has a "String" method, the
|
||||
default formatter for that type will use it and produce the output
|
||||
|
||||
77 Sunset Strip
|
||||
|
||||
Observe that the "String()" method calls "Sprint" (the obvious Go
|
||||
Observe that the "String" method calls "Sprint" (the obvious Go
|
||||
variant that returns a string) to do its formatting; special formatters
|
||||
can use the "fmt" library recursively.
|
||||
|
||||
@ -726,7 +726,7 @@ and such, but that's getting a little off the main thread so we'll leave it
|
||||
as an exploration exercise.
|
||||
|
||||
You might ask, though, how "Printf" can tell whether a type implements
|
||||
the "String()" method. Actually what it does is ask if the value can
|
||||
the "String" method. Actually what it does is ask if the value can
|
||||
be converted to an interface variable that implements the method.
|
||||
Schematically, given a value "v", it does this:
|
||||
|
||||
@ -765,7 +765,7 @@ interface type defined in the "io" library:
|
||||
|
||||
(This interface is another conventional name, this time for "Write"; there are also
|
||||
"io.Reader", "io.ReadWriter", and so on.)
|
||||
Thus you can call "Fprintf" on any type that implements a standard "Write()"
|
||||
Thus you can call "Fprintf" on any type that implements a standard "Write"
|
||||
method, not just files but also network channels, buffers, whatever
|
||||
you want.
|
||||
|
||||
|
Loading…
Reference in New Issue
Block a user