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| -rw-r--r-- | doc/go_for_cpp_programmers.html | 154 |
1 files changed, 92 insertions, 62 deletions
diff --git a/doc/go_for_cpp_programmers.html b/doc/go_for_cpp_programmers.html index 9920e016b..6786b7cca 100644 --- a/doc/go_for_cpp_programmers.html +++ b/doc/go_for_cpp_programmers.html @@ -81,14 +81,14 @@ easily from left to right. <pre> <b>Go C++</b> -var v1 int; // int v1; -var v2 string; // const std::string v2; (approximately) -var v3 [10]int; // int v3[10]; -var v4 []int; // int* v4; (approximately) -var v5 struct { f int }; // struct { int f; } v5; -var v6 *int; // int* v6; (but no pointer arithmetic) -var v7 map[string]int; // unordered_map<string, int>* v7; (approximately) -var v8 func(a int) int; // int (*v8)(int a); +var v1 int // int v1; +var v2 string // const std::string v2; (approximately) +var v3 [10]int // int v3[10]; +var v4 []int // int* v4; (approximately) +var v5 struct { f int } // struct { int f; } v5; +var v6 *int // int* v6; (but no pointer arithmetic) +var v7 map[string]int // unordered_map<string, int>* v7; (approximately) +var v8 func(a int) int // int (*v8)(int a); </pre> <p> @@ -106,7 +106,7 @@ parentheses. <pre> var ( - i int; + i int m float ) </pre> @@ -117,7 +117,7 @@ or not provide a name for any parameter; you can't omit some names and provide others. You may group several names with the same type: <pre> -func f(i, j, k int, s, t string); +func f(i, j, k int, s, t string) </pre> <p> @@ -127,7 +127,7 @@ not specified, the type of the variable is the type of the initialization expression. <pre> -var v = *p; +var v = *p </pre> <p> @@ -142,21 +142,21 @@ Within a function, a short declaration syntax is available with <code>:=</code> . <pre> -v1 := v2; +v1 := v2 </pre> <p> This is equivalent to <pre> -var v1 = v2; +var v1 = v2 </pre> <p> Go permits multiple assignments, which are done in parallel. <pre> -i, j = j, i; // Swap i and j. +i, j = j, i // Swap i and j. </pre> <p> @@ -165,19 +165,49 @@ parentheses. The returned values can be stored by assignment to a list of variables. <pre> -func f() (i int, j int); -v1, v2 = f(); +func f() (i int, j int) { ... } +v1, v2 = f() </pre> <p> -Go treats semicolons as separators, not terminators. Moreover, -semicolons may be omitted after the closing parenthesis of a declaration -block or after a closing brace that is not part of an expression -(e.g., <code>var s struct {}</code> or <code>{ x++ }</code>). -Semicolons are never required at the -top level of a file (between global declarations). However, they are -always <em>permitted</em> at -the end of a statement, so you can continue using them as in C++. +Go code uses very few semicolons in practice. Technically, all Go +statements are terminated by a semicolon. However, Go treats the end +of a non-blank line as a semicolon unless the line is clearly +incomplete (the exact rules are +in <a href="go_spec.html#Semicolons">the language specification</a>). +A consequence of this is that in some cases Go does not permit you to +use a line break. For example, you may not write +<pre> +func g() +{ // INVALID +} +</pre> +A semicolon will be inserted after <code>g()</code>, causing it to be +a function declaration rather than a function definition. Similarly, +you may not write +<pre> +if x { +} +else { // INVALID +} +</pre> +A semicolon will be inserted after the <code>}</code> preceding +the <code>else</code>, causing a syntax error. + +<p> +Since semicolons do end statements, you may continue using them as in +C++. However, that is not the recommended style. Idiomatic Go code +omits unnecessary semicolons, which in practice is all of them other +than the initial <for> loop clause and cases where you want several +short statements on a single line. + +<p> +While we're on the topic, we recommend that rather than worry about +semicolons and brace placement, you format your code with +the <code>gofmt</code> program. That will produce a single standard +Go style, and let you worry about your code rather than your +formatting. While the style may initially seem odd, it is as good as +any other style, and familiarity will lead to comfort. <p> When using a pointer to a struct, you use <code>.</code> instead @@ -187,8 +217,8 @@ are used in the same way. <pre> type myStruct struct { i int } -var v9 myStruct; // v9 has structure type -var p9 *myStruct; // p9 is a pointer to a structure +var v9 myStruct // v9 has structure type +var p9 *myStruct // p9 is a pointer to a structure f(v9.i, p9.i) </pre> @@ -199,11 +229,11 @@ statement, or the expressions of a <code>for</code> statement, or the value of a around the body of an <code>if</code> or <code>for</code> statement. <pre> -if a < b { f() } // Valid -if (a < b) { f() } // Valid (condition is a parenthesized expression) -if (a < b) f(); // INVALID -for i = 0; i < 10; i++ {} // Valid -for (i = 0; i < 10; i++) {} // INVALID +if a < b { f() } // Valid +if (a < b) { f() } // Valid (condition is a parenthesized expression) +if (a < b) f() // INVALID +for i = 0; i < 10; i++ {} // Valid +for (i = 0; i < 10; i++) {} // INVALID </pre> <p> @@ -272,8 +302,8 @@ The <code>defer</code> statement may be used to call a function after the function containing the <code>defer</code> statement returns. <pre> -fd := open("filename"); -defer close(fd); // fd will be closed when this function returns. +fd := open("filename") +defer close(fd) // fd will be closed when this function returns. </pre> <h2 id="Constants">Constants </h2> @@ -289,7 +319,7 @@ requires a typed value. This permits constants to be used relatively freely without requiring general implicit type conversion. <pre> -var a uint; +var a uint f(a + 1) // untyped numeric constant "1" becomes typed as uint </pre> @@ -299,7 +329,7 @@ numeric constant or constant expression. A limit is only applied when a constant is used where a type is required. <pre> -const huge = 1 << 100; +const huge = 1 << 100 f(huge >> 98) </pre> @@ -312,8 +342,8 @@ it reuses the preceding expression. <pre> const ( - red = iota; // red == 0 - blue; // blue == 1 + red = iota // red == 0 + blue // blue == 1 green // green == 2 ) </pre> @@ -344,7 +374,7 @@ capacity of the new slice is simply the capacity of <code>a</code> minus <code>I</code>. The capacity of an array is the length of the array. You may also assign an array pointer to a variable of slice type; given <code>var s []int; var a[10] int</code>, -the assignment <code>s = &a</code> is equivalent to +the assignment <code>s = &a</code> is equivalent to <code>s = a[0:len(a)]</code>. <p> @@ -452,8 +482,8 @@ Given this interface: <pre> type myInterface interface { - get() int; - set(i int); + get() int + set(i int) } </pre> @@ -472,8 +502,8 @@ variable of type <code>*myType</code>. <pre> func getAndSet(x myInterface) {} func f1() { - var p myType; - getAndSet(&p); + var p myType + getAndSet(&p) } </pre> @@ -499,7 +529,7 @@ This effectively implements <code>myChildType</code> as a child of <pre> func f2() { - var p myChildType; + var p myChildType getAndSet(&p) } </pre> @@ -531,7 +561,7 @@ not need to be any declared relationship between the two interfaces. <pre> type myPrintInterface interface { - print(); + print() } func f3(x myInterface) { x.(myPrintInterface).print() // type assertion to myPrintInterface @@ -563,10 +593,10 @@ at runtime, but all operations will involve a function call. <pre> type iterator interface { - get() Any; - set(v Any); - increment(); - equal(arg *iterator) bool; + get() Any + set(v Any) + increment() + equal(arg *iterator) bool } </pre> @@ -587,12 +617,12 @@ about these details. <pre> func server(i int) { for { - print(i); + print(i) sys.sleep(10) } } -go server(1); -go server(2); +go server(1) +go server(2) </pre> <p> @@ -607,12 +637,12 @@ Function literals (which Go implements as closures) can be useful with the <code>go</code> statement. <pre> -var g int; +var g int go func(i int) { s := 0 for j := 0; j < i; j++ { s += j } - g = s; -}(1000); // Passes argument 1000 to the function literal. + g = s +}(1000) // Passes argument 1000 to the function literal. </pre> <h2 id="Channels">Channels</h2> @@ -635,10 +665,10 @@ single value. <pre> type cmd struct { get bool; val int } func manager(ch chan cmd) { - var val int = 0; + var val int = 0 for { c := <- ch - if c.get { c.val = val; ch <- c } + if c.get { c.val = val ch <- c } else { val = c.val } } } @@ -653,9 +683,9 @@ instead. A solution is to pass in a channel. <pre> -type cmd2 struct { get bool; val int; ch <- chan int; } +type cmd2 struct { get bool; val int; ch <- chan int } func manager2(ch chan cmd2) { - var val int = 0; + var val int = 0 for { c := <- ch if c.get { c.ch <- val } @@ -669,9 +699,9 @@ To use <code>manager2</code>, given a channel to it: <pre> func f4(ch <- chan cmd2) int { - myCh := make(chan int); - c := cmd2{ true, 0, myCh }; // Composite literal syntax. - ch <- c; - return <-myCh; + myCh := make(chan int) + c := cmd2{ true, 0, myCh } // Composite literal syntax. + ch <- c + return <-myCh } </pre> |