diff options
Diffstat (limited to 'go.html.markdown')
| -rw-r--r-- | go.html.markdown | 79 |
1 files changed, 52 insertions, 27 deletions
diff --git a/go.html.markdown b/go.html.markdown index a1be08af..17f10bd9 100644 --- a/go.html.markdown +++ b/go.html.markdown @@ -12,7 +12,7 @@ contributors: - ["Alexej Friesen", "https://github.com/heyalexej"] --- -Go was created out of the need to get work done. It's not the latest trend +Go was created out of the need to get work done. It's not the latest trend in computer science, but it is the newest fastest way to solve real-world problems. @@ -26,7 +26,7 @@ Go comes with a great standard library and an enthusiastic community. ```go // Single line comment /* Multi- - line comment */ + line comment */ // A package clause starts every source file. // Main is a special name declaring an executable rather than a library. @@ -41,8 +41,8 @@ import ( "strconv" // String conversions. ) -// A function definition. Main is special. It is the entry point for the -// executable program. Love it or hate it, Go uses brace brackets. +// A function definition. Main is special. It is the entry point for the +// executable program. Love it or hate it, Go uses brace brackets. func main() { // Println outputs a line to stdout. // Qualify it with the package name, fmt. @@ -72,13 +72,13 @@ func learnMultiple(x, y int) (sum, prod int) { // Some built-in types and literals. func learnTypes() { // Short declaration usually gives you what you want. - s := "Learn Go!" // string type. + str := "Learn Go!" // string type. s2 := `A "raw" string literal 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 int32, 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 float64's. @@ -92,17 +92,32 @@ can include line breaks.` // Same string type. // 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. + a3 := [...]int{3, 1, 5} // An array initialized with a fixed size of three + // elements, with values 3, 1, and 5. - // Slices have dynamic size. Arrays and slices each have advantages + // 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. + 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. + // Because they are dynamic, slices can be appended to on-demand. + // To append elements to a slice, built-in append() function is used. + // First argument is a slice to which we are appending. Commonly, + // the array variable is updated in place, as in example below. + s := []int{1, 2, 3} // Result is a slice of length 3. + s = append(s, 4, 5, 6) // Added 3 elements. Slice now has length of 6. + fmt.Println(s) // Updated slice is now [1 2 3 4 5 6] + // To append another slice, instead of list of atomic elements we can + // pass a reference to a slice or a slice literal like this, with a + // trailing elipsis, meaning take a slice and unpack its elements, + // appending them to slice s. + s = append(s, []int{7, 8, 9}...) // Second argument is a slice literal. + fmt.Println(s) // Updated slice is now [1 2 3 4 5 6 7 8 9] + p, q := learnMemory() // Declares p, q to be type pointer to int. - fmt.Println(*p, *q) // * follows a pointer. This prints two ints. + fmt.Println(*p, *q) // * follows a pointer. This prints two ints. // Maps are a dynamically growable associative array type, like the // hash or dictionary types of some other languages. @@ -111,7 +126,7 @@ can include line breaks.` // Same string type. // Unused variables are an error in Go. // The underbar lets you "use" a variable but discard its value. - _, _, _, _, _, _, _, _, _ = s2, g, f, u, pi, n, a3, s4, bs + _, _, _, _, _, _, _, _, _, _ = str, s2, g, f, u, pi, n, a3, s4, bs // Output of course counts as using a variable. fmt.Println(s, c, a4, s3, d2, m) @@ -128,7 +143,7 @@ func learnNamedReturns(x, y int) (z int) { return // z is implicit here, because we named it earlier. } -// Go is fully garbage collected. It has pointers but no pointer arithmetic. +// 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. @@ -177,6 +192,14 @@ func learnFlowControl() { break // Just kidding. continue // Unreached. } + + // You can use range to iterate over an array, a slice, a string, a map, or a channel. + // range returns one (channel) or two values (array, slice, string and map). + for key, value := range map[string]int{"one": 1, "two": 2, "three": 3} { + // for each pair in the map, print key and value + fmt.Printf("key=%s, value=%d\n", key, value) + } + // As with for, := in an if statement means to declare and assign // y first, then test y > x. if y := expensiveComputation(); y > x { @@ -198,7 +221,7 @@ func learnFlowControl() { func(a, b int) int { return (a + b) * 2 }(10, 2)) // Called with args 10 and 2 - // => Add + double two numbers: 24 + // => Add + double two numbers: 24 // When you need it, you'll love it. goto love @@ -245,7 +268,7 @@ type pair struct { x, y int } -// Define a method on type pair. Pair now implements Stringer. +// Define a method on type pair. Pair now implements Stringer. func (p pair) String() string { // p is called the "receiver" // Sprintf is another public function in package fmt. // Dot syntax references fields of p. @@ -253,13 +276,13 @@ func (p pair) String() string { // p is called the "receiver" } func learnInterfaces() { - // Brace syntax is a "struct literal." It evaluates to an initialized - // struct. The := syntax declares and initializes p to this struct. + // 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 - // Call String method of i, of type Stringer. Output same as above. + // 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 @@ -297,7 +320,7 @@ func learnErrorHandling() { // prints 'strconv.ParseInt: parsing "non-int": invalid syntax' fmt.Println(err) } - // We'll revisit interfaces a little later. Meanwhile, + // We'll revisit interfaces a little later. Meanwhile, learnConcurrency() } @@ -308,12 +331,12 @@ func inc(i int, c chan int) { // We'll use inc to increment some numbers concurrently. func learnConcurrency() { - // Same make function used earlier to make a slice. Make allocates and + // Same make function used earlier to make a slice. Make allocates and // initializes slices, maps, and channels. c := make(chan int) - // Start three concurrent goroutines. Numbers will be incremented + // Start three concurrent goroutines. Numbers will be incremented // concurrently, perhaps in parallel if the machine is capable and - // properly configured. All three send to the same channel. + // properly configured. All three send to the same channel. go inc(0, c) // go is a statement that starts a new goroutine. go inc(10, c) go inc(-805, c) @@ -326,7 +349,7 @@ func learnConcurrency() { 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 + // 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, @@ -336,7 +359,7 @@ func learnConcurrency() { 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 + // At this point a value was taken from either c or cs. One of the two // goroutines started above has completed, the other will remain blocked. learnWebProgramming() // Go does it. You want to do it too. @@ -375,13 +398,15 @@ func requestServer() { The root of all things Go is the [official Go web site](http://golang.org/). There you can follow the tutorial, play interactively, and read lots. -The language definition itself is highly recommended. It's easy to read +The language definition itself is highly recommended. It's easy to read and amazingly short (as language definitions go these days.) +You can play around with the code on [Go playground](https://play.golang.org/p/tnWMjr16Mm). Try to change it and run it from your browser! Note that you can use [https://play.golang.org](https://play.golang.org) as a [REPL](https://en.wikipedia.org/wiki/Read-eval-print_loop) to test things and code in your browser, without even installing Go. + On the reading list for students of Go is the [source code to the standard -library](http://golang.org/src/pkg/). Comprehensively documented, it +library](http://golang.org/src/pkg/). Comprehensively documented, it demonstrates the best of readable and understandable Go, Go style, and Go -idioms. Or you can click on a function name in [the +idioms. Or you can click on a function name in [the documentation](http://golang.org/pkg/) and the source code comes up! Another great resource to learn Go is [Go by example](https://gobyexample.com/). |