diff options
| -rw-r--r-- | go.html.markdown | 146 |
1 files changed, 75 insertions, 71 deletions
diff --git a/go.html.markdown b/go.html.markdown index d68ba51b..d1a0ae34 100644 --- a/go.html.markdown +++ b/go.html.markdown @@ -6,6 +6,7 @@ filename: learngo.go contributors: - ["Sonia Keys", "https://github.com/soniakeys"] - ["Christopher Bess", "https://github.com/cbess"] + - ["Jesse Johnson", "https://github.com/holocronweaver"] --- Go was created out of the need to get work done. It's not the latest trend @@ -30,9 +31,10 @@ package main // Import declaration declares library packages referenced in this file. import ( - "fmt" // A package in the Go standard library + "fmt" // A package in the Go standard library. "net/http" // Yes, a web server! - "strconv" // String conversions + "strconv" // String conversions. + m "math" // Math library with local alias m. ) // A function definition. Main is special. It is the entry point for the @@ -53,49 +55,49 @@ func beyondHello() { x = 3 // Variable assignment. // "Short" declarations use := to infer the type, declare, and assign. y := 4 - sum, prod := learnMultiple(x, y) // function returns two values - fmt.Println("sum:", sum, "prod:", prod) // simple output + sum, prod := learnMultiple(x, y) // Function returns two values. + fmt.Println("sum:", sum, "prod:", prod) // Simple output. learnTypes() // < y minutes, learn more! } // Functions can have parameters and (multiple!) return values. func learnMultiple(x, y int) (sum, prod int) { - return x + y, x * y // return two values + return x + y, x * y // Return two values. } // Some built-in types and literals. func learnTypes() { // Short declaration usually gives you what you want. - s := "Learn Go!" // string type + s := "Learn Go!" // string type. s2 := `A "raw" string literal -can include line breaks.` // same string type +can include line breaks.` // Same string type. - // non-ASCII literal. Go source is UTF-8. - g := 'Σ' // rune type, an alias for uint32, holds a unicode code point + // Non-ASCII literal. Go source is UTF-8. + g := 'Σ' // rune type, an alias for uint32, holds a unicode code point. - f := 3.14195 // float64, an IEEE-754 64-bit floating point number - c := 3 + 4i // complex128, represented internally with two float64s + f := 3.14195 // float64, an IEEE-754 64-bit floating point number. + c := 3 + 4i // complex128, represented internally with two float64's. // Var syntax with an initializers. - var u uint = 7 // unsigned, but implementation dependent size as with int + var u uint = 7 // Unsigned, but implementation dependent size as with int. var pi float32 = 22. / 7 // Conversion syntax with a short declaration. - n := byte('\n') // byte is an alias for uint8 + n := byte('\n') // byte is an alias for uint8. // Arrays have size fixed at compile time. - var a4 [4]int // an array of 4 ints, initialized to all 0 - a3 := [...]int{3, 1, 5} // an array of 3 ints, initialized as shown + var a4 [4]int // An array of 4 ints, initialized to all 0. + a3 := [...]int{3, 1, 5} // An array of 3 ints, initialized as shown. // Slices have dynamic size. Arrays and slices each have advantages // but use cases for slices are much more common. - s3 := []int{4, 5, 9} // compare to a3. no ellipsis here - s4 := make([]int, 4) // allocates slice of 4 ints, initialized to all 0 - var d2 [][]float64 // declaration only, nothing allocated here - bs := []byte("a slice") // type conversion syntax + s3 := []int{4, 5, 9} // Compare to a3. No ellipsis here. + s4 := make([]int, 4) // Allocates slice of 4 ints, initialized to all 0. + var d2 [][]float64 // Declaration only, nothing allocated here. + bs := []byte("a slice") // Type conversion syntax. - p, q := learnMemory() // declares p, q to be type pointer to int. + p, q := learnMemory() // Declares p, q to be type pointer to int. fmt.Println(*p, *q) // * follows a pointer. This prints two ints. // Maps are a dynamically growable associative array type, like the @@ -109,23 +111,23 @@ can include line breaks.` // same string type // Output of course counts as using a variable. fmt.Println(s, c, a4, s3, d2, m) - learnFlowControl() // back in the flow + learnFlowControl() // Back in the flow. } // Go is fully garbage collected. It has pointers but no pointer arithmetic. // You can make a mistake with a nil pointer, but not by incrementing a pointer. func learnMemory() (p, q *int) { // Named return values p and q have type pointer to int. - p = new(int) // built-in function new allocates memory. + p = new(int) // Built-in function new allocates memory. // The allocated int is initialized to 0, p is no longer nil. - s := make([]int, 20) // allocate 20 ints as a single block of memory - s[3] = 7 // assign one of them - r := -2 // declare another local variable + s := make([]int, 20) // Allocate 20 ints as a single block of memory. + s[3] = 7 // Assign one of them. + r := -2 // Declare another local variable. return &s[3], &r // & takes the address of an object. } -func expensiveComputation() int { - return 1e6 +func expensiveComputation() float64 { + return m.Exp(10) } func learnFlowControl() { @@ -135,29 +137,31 @@ func learnFlowControl() { } // Formatting is standardized by the command line command "go fmt." if false { - // pout + // Pout. } else { - // gloat + // Gloat. } // Use switch in preference to chained if statements. - x := 1 + x := 42.0 switch x { case 0: case 1: - // cases don't "fall through" - case 2: - // unreached + case 42: + // Cases don't "fall through". + case 43: + // Unreached. } // Like if, for doesn't use parens either. - for x := 0; x < 3; x++ { // ++ is a statement + // Variables declared in for and if are local to their scope. + for x := 0; x < 3; x++ { // ++ is a statement. fmt.Println("iteration", x) } - // x == 1 here. + // x == 42 here. // For is the only loop statement in Go, but it has alternate forms. - for { // infinite loop - break // just kidding - continue // unreached + for { // Infinite loop. + break // Just kidding. + continue // Unreached. } // As with for, := in an if statement means to declare and assign y first, // then test y > x. @@ -166,30 +170,17 @@ func learnFlowControl() { } // Function literals are closures. xBig := func() bool { - return x > 100 // references x declared above switch statement. + return x > 100 // References x declared above switch statement. } - fmt.Println("xBig:", xBig()) // true (we last assigned 1e6 to x) - x /= 1e5 // this makes it == 10 - fmt.Println("xBig:", xBig()) // false now + fmt.Println("xBig:", xBig()) // true (we last assigned 1e6 to x). + x /= m.Exp(9) // This makes x == e. + fmt.Println("xBig:", xBig()) // false now. // When you need it, you'll love it. goto love love: - // Good stuff coming up! - learnVariadicParams("great", "learning", "here!") - learnInterfaces() -} - -// Functions can have variadic parameters -func learnVariadicParams(myStrings ...string) { - // iterate each value of the variadic - for _, param := range myStrings { - fmt.Println("param:", param) - } - - // pass variadic value as a variadic parameter - fmt.Println("params:", fmt.Sprintln(myStrings...)) + learnInterfaces() // Good stuff coming up! } // Define Stringer as an interface type with one method, String. @@ -213,16 +204,29 @@ func learnInterfaces() { // Brace syntax is a "struct literal." It evaluates to an initialized // struct. The := syntax declares and initializes p to this struct. p := pair{3, 4} - fmt.Println(p.String()) // call String method of p, of type pair. - var i Stringer // declare i of interface type Stringer. - i = p // valid because pair implements Stringer + fmt.Println(p.String()) // Call String method of p, of type pair. + var i Stringer // Declare i of interface type Stringer. + i = p // Valid because pair implements Stringer // Call String method of i, of type Stringer. Output same as above. fmt.Println(i.String()) // Functions in the fmt package call the String method to ask an object // for a printable representation of itself. - fmt.Println(p) // output same as above. Println calls String method. - fmt.Println(i) // output same as above + fmt.Println(p) // Output same as above. Println calls String method. + fmt.Println(i) // Output same as above. + + learnVariadicParams("great", "learning", "here!") +} + +// Functions can have variadic parameters. +func learnVariadicParams(myStrings ...interface{}) { + // Iterate each value of the variadic. + for _, param := range myStrings { + fmt.Println("param:", param) + } + + // Pass variadic value as a variadic parameter. + fmt.Println("params:", fmt.Sprintln(myStrings...)) learnErrorHandling() } @@ -237,7 +241,7 @@ func learnErrorHandling() { } // An error value communicates not just "ok" but more about the problem. if _, err := strconv.Atoi("non-int"); err != nil { // _ discards value - // prints "strconv.ParseInt: parsing "non-int": invalid syntax" + // prints 'strconv.ParseInt: parsing "non-int": invalid syntax' fmt.Println(err) } // We'll revisit interfaces a little later. Meanwhile, @@ -264,19 +268,19 @@ func learnConcurrency() { // There is no telling in what order the results will arrive! fmt.Println(<-c, <-c, <-c) // channel on right, <- is "receive" operator. - cs := make(chan string) // another channel, this one handles strings. - cc := make(chan chan string) // a channel of string channels. - go func() { c <- 84 }() // start a new goroutine just to send a value - go func() { cs <- "wordy" }() // again, for cs this time + cs := make(chan string) // Another channel, this one handles strings. + ccs := make(chan chan string) // A channel of string channels. + go func() { c <- 84 }() // Start a new goroutine just to send a value. + go func() { cs <- "wordy" }() // Again, for cs this time. // Select has syntax like a switch statement but each case involves // a channel operation. It selects a case at random out of the cases // that are ready to communicate. select { - case i := <-c: // the value received can be assigned to a variable + case i := <-c: // The value received can be assigned to a variable, fmt.Printf("it's a %T", i) - case <-cs: // or the value received can be discarded + case <-cs: // or the value received can be discarded. fmt.Println("it's a string") - case <-cc: // empty channel, not ready for communication. + case <-ccs: // Empty channel, not ready for communication. fmt.Println("didn't happen.") } // At this point a value was taken from either c or cs. One of the two @@ -287,7 +291,7 @@ func learnConcurrency() { // A single function from package http starts a web server. func learnWebProgramming() { - // ListenAndServe first parameter is TCP address to listen at. + // First parameter of ListenAndServe is TCP address to listen to. // Second parameter is an interface, specifically http.Handler. err := http.ListenAndServe(":8080", pair{}) fmt.Println(err) // don't ignore errors @@ -295,7 +299,7 @@ func learnWebProgramming() { // Make pair an http.Handler by implementing its only method, ServeHTTP. func (p pair) ServeHTTP(w http.ResponseWriter, r *http.Request) { - // Serve data with a method of http.ResponseWriter + // Serve data with a method of http.ResponseWriter. w.Write([]byte("You learned Go in Y minutes!")) } ``` |