mirror of
https://github.com/golang/go
synced 2024-11-21 15:24:45 -07:00
Minor cleanups.
These are all fairly trivial and may be ignored. R=r CC=go-dev http://go/go-review/1024025
This commit is contained in:
parent
ceb6031ecd
commit
97a55a7485
@ -31,12 +31,13 @@ Let's start in the usual way:
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</pre>
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<p>
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Every Go source file declares, using a <code>package</code> statement, which package it's part of.
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The <code>main</code> package's <code>main</code> function is where the program starts running (after
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any initialization). It may also import other packages to use their facilities.
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It may also import other packages to use their facilities.
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This program imports the package <code>fmt</code> to gain access to
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our old, now capitalized and package-qualified friend, <code>fmt.Printf</code>.
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our old, now capitalized and package-qualified, friend, <code>fmt.Printf</code>.
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<p>
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Function declarations are introduced with the <code>func</code> keyword.
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Functions are introduced with the <code>func</code> keyword.
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The <code>main</code> package's <code>main</code> function is where the program starts running (after
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any initialization).
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<p>
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String constants can contain Unicode characters, encoded in UTF-8.
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(In fact, Go source files are defined to be encoded in UTF-8.)
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@ -127,7 +128,7 @@ But it's not necessary to do so; we could have said
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</pre>
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<p>
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Semicolons aren't needed here; in fact, semicolons are unnecessary after any
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top-level declaration, even though they are needed as separators <i>within</i>
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top-level declaration, although they are needed as separators <i>within</i>
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a parenthesized list of declarations.
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<p>
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This program imports the <code>"os"</code> package to access its <code>Stdout</code> variable, of type
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@ -213,14 +214,14 @@ started; for instance, <code>os.Args</code> is a slice used by the
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<p>
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Go has some familiar types such as <code>int</code> and <code>float</code>, which represent
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values of the ''appropriate'' size for the machine. It also defines
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specifically-sized types such as <code>int8</code>, <code>float64</code>, and so on, plus
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explicitly-sized types such as <code>int8</code>, <code>float64</code>, and so on, plus
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unsigned integer types such as <code>uint</code>, <code>uint32</code>, etc. These are
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distinct types; even if <code>int</code> and <code>int32</code> are both 32 bits in size,
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they are not the same type. There is also a <code>byte</code> synonym for
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<code>uint8</code>, which is the element type for strings.
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<p>
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Speaking of <code>string</code>, that's a built-in type as well. Strings are
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<i>immutable values</i> - they are not just arrays of <code>byte</code> values.
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<i>immutable values</i>—they are not just arrays of <code>byte</code> values.
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Once you've built a string <i>value</i>, you can't change it, although
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of course you can change a string <i>variable</i> simply by
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reassigning it. This snippet from <code>strings.go</code> is legal code:
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@ -302,8 +303,11 @@ and invoke it like this:
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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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after the parameter list.
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The expression <code>[3]int{1,2,3}</code> - a type followed by a brace-bounded expression
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- is a constructor for a value, in this case an array of 3 <code>ints</code>. Putting an <code>&</code>
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The expression <code>[3]int{1,2,3}</code>—a type followed by a
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brace-bounded
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expression—is a constructor for a value, in this case an array
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of 3 <code>ints</code>.
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Putting an <code>&</code>
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in front gives us the address of a unique instance of the value. We pass the
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pointer to <code>sum()</code> by (implicitly) promoting it to a slice.
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<p>
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@ -315,7 +319,8 @@ elements for you, use <code>...</code> as the array size:
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</pre>
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<p>
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In practice, though, unless you're meticulous about storage layout within a
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data structure, a slice itself - using empty brackets and no <code>&</code> - is all you need:
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data structure, a slice itself—using empty brackets and no
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<code>&</code>—is all you need:
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<p>
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<pre>
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s := sum([]int{1,2,3});
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@ -351,7 +356,7 @@ or the more idiomatic
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t := new(T);
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</pre>
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<p>
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Some types - maps, slices, and channels (see below) - have reference semantics.
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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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@ -368,12 +373,12 @@ 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 of 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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you receive a pointer to an uninitialized reference, equivalent to
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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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<h2>An Interlude about Constants</h2>
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@ -393,7 +398,7 @@ language specification but here are some illustrative examples:
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<p>
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<pre>
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var a uint64 = 0 // a has type uint64, value 0
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a := uint64(0) // equivalent; use a "conversion"
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a := uint64(0) // equivalent; uses a "conversion"
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i := 0x1234 // i gets default type: int
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var j int = 1e6 // legal - 1000000 is representable in an int
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x := 1.5 // a float
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@ -426,8 +431,9 @@ sort of open/close/read/write interface. Here's the start of <code>file.go</cod
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15 }
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</pre>
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<p>
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The first few lines declare the name of the package - <code>file</code> -
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and then import two packages. The <code>os</code> package hides the differences
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The first few lines declare the name of the
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package—<code>file</code>—and then import two packages. The <code>os</code>
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package hides the differences
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between various operating systems to give a consistent view of files and
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so on; here we're going to use its error handling utilities
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and reproduce the rudiments of its file I/O.
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@ -671,7 +677,7 @@ 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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they all have the same type.
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<p>
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Since the <code>switch</code> value is just <code>true</code>, we could leave it off - as is also
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Since the <code>switch</code> value is just <code>true</code>, we could leave it off—as is also
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the situation
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in a <code>for</code> statement, a missing value means <code>true</code>. In fact, such a <code>switch</code>
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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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@ -695,8 +701,8 @@ Here is code from <code>progs/cat_rot13.go</code>:
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29 }
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</pre>
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<p>
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Any type that has the two methods of <code>reader</code> - regardless of whatever
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other methods the type may also have - is said to <i>implement</i> the
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Any type that has the two methods of <code>reader</code>—regardless of whatever
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other methods the type may also have—is said to <i>implement</i> the
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interface. Since <code>file.File</code> implements these methods, it implements the
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<code>reader</code> interface. We could tweak the <code>cat</code> subroutine to accept a <code>reader</code>
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instead of a <code>*file.File</code> and it would work just fine, but let's embellish a little
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@ -1011,7 +1017,7 @@ operations such as type conversion, map update, communications, and so on,
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although this is the only appearance in this tutorial.)
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If the value does not satisfy the interface, <code>ok</code> will be false.
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<p>
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In this snippet the name <code>Stringer</code> follows the convention that we add <code>[e]r</code>
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In this snippet the name <code>Stringer</code> follows the convention that we add ''[e]r''
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to interfaces describing simple method sets like this.
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<p>
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One last wrinkle. To complete the suite, besides <code>Printf</code> etc. and <code>Sprintf</code>
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@ -1033,11 +1039,11 @@ you want.
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<p>
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<h2>Prime numbers</h2>
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<p>
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Now we come to processes and communication - concurrent programming.
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Now we come to processes and communication—concurrent programming.
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It's a big subject so to be brief we assume some familiarity with the topic.
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<p>
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A classic program in the style is a prime sieve.
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(The sieve of Eratosthenes is computationationally more efficient than
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(The sieve of Eratosthenes is computationally more efficient than
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the algorithm presented here, but we are more interested in concurrency than
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algorithmics at the moment.)
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It works by taking a stream of all the natural numbers and introducing
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@ -1099,7 +1105,7 @@ operator <code><-</code> (receive) retrieves the next value on the channel.
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<p>
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The generator and filters execute concurrently. Go has
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its own model of process/threads/light-weight processes/coroutines,
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so to avoid notational confusion we'll call concurrently executing
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so to avoid notational confusion we call concurrently executing
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computations in Go <i>goroutines</i>. To start a goroutine,
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invoke the function, prefixing the call with the keyword <code>go</code>;
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this starts the function running in parallel with the current
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@ -25,12 +25,13 @@ Let's start in the usual way:
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--PROG progs/helloworld.go /package/ END
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Every Go source file declares, using a "package" statement, which package it's part of.
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The "main" package's "main" function is where the program starts running (after
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any initialization). It may also import other packages to use their facilities.
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It may also import other packages to use their facilities.
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This program imports the package "fmt" to gain access to
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our old, now capitalized and package-qualified friend, "fmt.Printf".
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our old, now capitalized and package-qualified, friend, "fmt.Printf".
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Function declarations are introduced with the "func" keyword.
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Functions are introduced with the "func" keyword.
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The "main" package's "main" function is where the program starts running (after
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any initialization).
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String constants can contain Unicode characters, encoded in UTF-8.
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(In fact, Go source files are defined to be encoded in UTF-8.)
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@ -86,7 +87,7 @@ But it's not necessary to do so; we could have said
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const Newline = "\n"
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Semicolons aren't needed here; in fact, semicolons are unnecessary after any
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top-level declaration, even though they are needed as separators <i>within</i>
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top-level declaration, although they are needed as separators <i>within</i>
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a parenthesized list of declarations.
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This program imports the ""os"" package to access its "Stdout" variable, of type
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@ -163,14 +164,14 @@ An Interlude about Types
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Go has some familiar types such as "int" and "float", which represent
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values of the ''appropriate'' size for the machine. It also defines
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specifically-sized types such as "int8", "float64", and so on, plus
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explicitly-sized types such as "int8", "float64", and so on, plus
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unsigned integer types such as "uint", "uint32", etc. These are
|
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distinct types; even if "int" and "int32" are both 32 bits in size,
|
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they are not the same type. There is also a "byte" synonym for
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"uint8", which is the element type for strings.
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Speaking of "string", that's a built-in type as well. Strings are
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<i>immutable values</i> - they are not just arrays of "byte" values.
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<i>immutable values</i>—they are not just arrays of "byte" values.
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Once you've built a string <i>value</i>, you can't change it, although
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of course you can change a string <i>variable</i> simply by
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reassigning it. This snippet from "strings.go" is legal code:
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@ -232,8 +233,11 @@ and invoke it like this:
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Note how the return type ("int") is defined for "sum()" by stating it
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after the parameter list.
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The expression "[3]int{1,2,3}" - a type followed by a brace-bounded expression
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- is a constructor for a value, in this case an array of 3 "ints". Putting an "&"
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The expression "[3]int{1,2,3}"—a type followed by a
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brace-bounded
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expression—is a constructor for a value, in this case an array
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of 3 "ints".
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Putting an "&"
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in front gives us the address of a unique instance of the value. We pass the
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pointer to "sum()" by (implicitly) promoting it to a slice.
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@ -243,7 +247,8 @@ elements for you, use "..." as the array size:
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s := sum(&[...]int{1,2,3});
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|
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In practice, though, unless you're meticulous about storage layout within a
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data structure, a slice itself - using empty brackets and no "&" - is all you need:
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data structure, a slice itself—using empty brackets and no
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"&"—is all you need:
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s := sum([]int{1,2,3});
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@ -272,7 +277,7 @@ or the more idiomatic
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t := new(T);
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Some types - maps, slices, and channels (see below) - have reference semantics.
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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 "make()":
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@ -285,12 +290,12 @@ If you just declare the map, as in
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var m map[string]int;
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it creates a "nil" reference that cannot hold anything. To use the map,
|
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you must first initialize the reference using "make()" or by assignment of an
|
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you must first initialize the reference using "make()" or by assignment from an
|
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existing map.
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Note that "new(T)" returns type "*T" while "make(T)" returns type
|
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"T". If you (mistakenly) allocate a reference object with "new()",
|
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you receive a pointer to an uninitialized reference, equivalent to
|
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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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|
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An Interlude about Constants
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@ -308,7 +313,7 @@ There are nuances that deserve redirection to the legalese of the
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language specification but here are some illustrative examples:
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var a uint64 = 0 // a has type uint64, value 0
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a := uint64(0) // equivalent; use a "conversion"
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a := uint64(0) // equivalent; uses a "conversion"
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i := 0x1234 // i gets default type: int
|
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var j int = 1e6 // legal - 1000000 is representable in an int
|
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x := 1.5 // a float
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@ -329,8 +334,9 @@ sort of open/close/read/write interface. Here's the start of "file.go":
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--PROG progs/file.go /package/ /^}/
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The first few lines declare the name of the package - "file" -
|
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and then import two packages. The "os" package hides the differences
|
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The first few lines declare the name of the
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package—"file"—and then import two packages. The "os"
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package hides the differences
|
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between various operating systems to give a consistent view of files and
|
||||
so on; here we're going to use its error handling utilities
|
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and reproduce the rudiments of its file I/O.
|
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@ -451,7 +457,7 @@ 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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they all have the same type.
|
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|
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Since the "switch" value is just "true", we could leave it off - as is also
|
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Since the "switch" value is just "true", we could leave it off—as is also
|
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the situation
|
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in a "for" statement, a missing value means "true". In fact, such a "switch"
|
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is a form of "if-else" chain. While we're here, it should be mentioned that in
|
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@ -470,8 +476,8 @@ Here is code from "progs/cat_rot13.go":
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--PROG progs/cat_rot13.go /type.reader/ /^}/
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|
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Any type that has the two methods of "reader" - regardless of whatever
|
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other methods the type may also have - is said to <i>implement</i> the
|
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Any type that has the two methods of "reader"—regardless of whatever
|
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other methods the type may also have—is said to <i>implement</i> the
|
||||
interface. Since "file.File" implements these methods, it implements the
|
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"reader" interface. We could tweak the "cat" subroutine to accept a "reader"
|
||||
instead of a "*file.File" and it would work just fine, but let's embellish a little
|
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@ -665,7 +671,7 @@ operations such as type conversion, map update, communications, and so on,
|
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although this is the only appearance in this tutorial.)
|
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If the value does not satisfy the interface, "ok" will be false.
|
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|
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In this snippet the name "Stringer" follows the convention that we add "[e]r"
|
||||
In this snippet the name "Stringer" follows the convention that we add ''[e]r''
|
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to interfaces describing simple method sets like this.
|
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|
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One last wrinkle. To complete the suite, besides "Printf" etc. and "Sprintf"
|
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@ -686,11 +692,11 @@ you want.
|
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Prime numbers
|
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----
|
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|
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Now we come to processes and communication - concurrent programming.
|
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Now we come to processes and communication—concurrent programming.
|
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It's a big subject so to be brief we assume some familiarity with the topic.
|
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|
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A classic program in the style is a prime sieve.
|
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(The sieve of Eratosthenes is computationationally more efficient than
|
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(The sieve of Eratosthenes is computationally more efficient than
|
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the algorithm presented here, but we are more interested in concurrency than
|
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algorithmics at the moment.)
|
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It works by taking a stream of all the natural numbers and introducing
|
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@ -734,7 +740,7 @@ operator "<-" (receive) retrieves the next value on the channel.
|
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|
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The generator and filters execute concurrently. Go has
|
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its own model of process/threads/light-weight processes/coroutines,
|
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so to avoid notational confusion we'll call concurrently executing
|
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so to avoid notational confusion we call concurrently executing
|
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computations in Go <i>goroutines</i>. To start a goroutine,
|
||||
invoke the function, prefixing the call with the keyword "go";
|
||||
this starts the function running in parallel with the current
|
||||
|
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