diff --git a/go.html.markdown b/go.html.markdown
index 0ecc6120..a1be08af 100644
--- a/go.html.markdown
+++ b/go.html.markdown
@@ -9,6 +9,7 @@ contributors:
- ["Jesse Johnson", "https://github.com/holocronweaver"]
- ["Quint Guvernator", "https://github.com/qguv"]
- ["Jose Donizetti", "https://github.com/josedonizetti"]
+ - ["Alexej Friesen", "https://github.com/heyalexej"]
---
Go was created out of the need to get work done. It's not the latest trend
@@ -33,87 +34,88 @@ package main
// Import declaration declares library packages referenced in this file.
import (
- "fmt" // A package in the Go standard library.
- "net/http" // Yes, a web server!
- "strconv" // String conversions.
- m "math" // Math library with local alias m.
+ "fmt" // A package in the Go standard library.
+ "io/ioutil" // Implements some I/O utility functions.
+ m "math" // Math library with local alias m.
+ "net/http" // Yes, a web server!
+ "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.
func main() {
- // Println outputs a line to stdout.
- // Qualify it with the package name, fmt.
- fmt.Println("Hello world!")
+ // Println outputs a line to stdout.
+ // Qualify it with the package name, fmt.
+ fmt.Println("Hello world!")
- // Call another function within this package.
- beyondHello()
+ // Call another function within this package.
+ beyondHello()
}
// Functions have parameters in parentheses.
// If there are no parameters, empty parentheses are still required.
func beyondHello() {
- var x int // Variable declaration. Variables must be declared before use.
- 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.
- learnTypes() // < y minutes, learn more!
+ var x int // Variable declaration. Variables must be declared before use.
+ 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.
+ 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.
+ // Short declaration usually gives you what you want.
+ s := "Learn Go!" // string type.
- s2 := `A "raw" string literal
+ 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 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 float64's.
+ 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 pi float32 = 22. / 7
+ // Var syntax with an initializers.
+ 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.
+ // Conversion syntax with a short declaration.
+ 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.
+ // 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.
- // 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.
+ // 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.
- p, q := learnMemory() // Declares p, q to be type pointer to int.
- fmt.Println(*p, *q) // * follows a pointer. This prints two ints.
+ 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
- // hash or dictionary types of some other languages.
- m := map[string]int{"three": 3, "four": 4}
- m["one"] = 1
+ // Maps are a dynamically growable associative array type, like the
+ // hash or dictionary types of some other languages.
+ m := map[string]int{"three": 3, "four": 4}
+ m["one"] = 1
- // 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
- // Output of course counts as using a variable.
- fmt.Println(s, c, a4, s3, d2, m)
+ // 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
+ // 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.
}
// It is possible, unlike in many other languages for functions in go
@@ -122,250 +124,249 @@ can include line breaks.` // Same string type.
// allows us to easily return from multiple points in a function as well as to
// only use the return keyword, without anything further.
func learnNamedReturns(x, y int) (z int) {
- z = x * y
- return // z is implicit here, because we named it earlier.
+ z = x * y
+ return // z is implicit here, because we named it earlier.
}
// 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.
- // 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.
- return &s[3], &r // & takes the address of an object.
+ // Named return values p and q have type pointer to int.
+ 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.
+ return &s[3], &r // & takes the address of an object.
}
func expensiveComputation() float64 {
- return m.Exp(10)
+ return m.Exp(10)
}
func learnFlowControl() {
- // If statements require brace brackets, and do not require parens.
- if true {
- fmt.Println("told ya")
- }
- // Formatting is standardized by the command line command "go fmt."
- if false {
- // Pout.
- } else {
- // Gloat.
- }
- // Use switch in preference to chained if statements.
- x := 42.0
- switch x {
- case 0:
- case 1:
- case 42:
- // Cases don't "fall through".
- case 43:
- // Unreached.
- }
- // Like if, for doesn't use parens either.
- // 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 == 42 here.
+ // If statements require brace brackets, and do not require parens.
+ if true {
+ fmt.Println("told ya")
+ }
+ // Formatting is standardized by the command line command "go fmt."
+ if false {
+ // Pout.
+ } else {
+ // Gloat.
+ }
+ // Use switch in preference to chained if statements.
+ x := 42.0
+ switch x {
+ case 0:
+ case 1:
+ case 42:
+ // Cases don't "fall through".
+ case 43:
+ // Unreached.
+ }
+ // Like if, for doesn't use parens either.
+ // 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 == 42 here.
- // For is the only loop statement in Go, but it has alternate forms.
- 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.
- if y := expensiveComputation(); y > x {
- x = y
- }
- // Function literals are closures.
- xBig := func() bool {
- return x > 10000 // References x declared above switch statement.
- }
- fmt.Println("xBig:", xBig()) // true (we last assigned e^10 to x).
- x = 1.3e3 // This makes x == 1300
- fmt.Println("xBig:", xBig()) // false now.
+ // For is the only loop statement in Go, but it has alternate forms.
+ 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.
+ if y := expensiveComputation(); y > x {
+ x = y
+ }
+ // Function literals are closures.
+ xBig := func() bool {
+ return x > 10000 // References x declared above switch statement.
+ }
+ fmt.Println("xBig:", xBig()) // true (we last assigned e^10 to x).
+ x = 1.3e3 // This makes x == 1300
+ fmt.Println("xBig:", xBig()) // false now.
- // What's more is function literals may be defined and called inline,
- // acting as an argument to function, as long as:
- // a) function literal is called immediately (),
- // b) result type matches expected type of argument.
- fmt.Println("Add + double two numbers: ",
- func(a, b int) int {
- return (a + b) * 2
- }(10, 2)) // Called with args 10 and 2
- // => Add + double two numbers: 24
-
- // When you need it, you'll love it.
- goto love
+ // What's more is function literals may be defined and called inline,
+ // acting as an argument to function, as long as:
+ // a) function literal is called immediately (),
+ // b) result type matches expected type of argument.
+ fmt.Println("Add + double two numbers: ",
+ func(a, b int) int {
+ return (a + b) * 2
+ }(10, 2)) // Called with args 10 and 2
+ // => Add + double two numbers: 24
+
+ // When you need it, you'll love it.
+ goto love
love:
- learnFunctionFactory() // func returning func is fun(3)(3)
- learnDefer() // A quick detour to an important keyword.
- learnInterfaces() // Good stuff coming up!
+ learnFunctionFactory() // func returning func is fun(3)(3)
+ learnDefer() // A quick detour to an important keyword.
+ learnInterfaces() // Good stuff coming up!
}
func learnFunctionFactory() {
- // Next two are equivalent, with second being more practical
- fmt.Println(sentenceFactory("summer")("A beautiful", "day!"))
+ // Next two are equivalent, with second being more practical
+ fmt.Println(sentenceFactory("summer")("A beautiful", "day!"))
- d := sentenceFactory("summer")
- fmt.Println(d("A beautiful", "day!"))
- fmt.Println(d("A lazy", "afternoon!"))
+ d := sentenceFactory("summer")
+ fmt.Println(d("A beautiful", "day!"))
+ fmt.Println(d("A lazy", "afternoon!"))
}
// Decorators are common in other languages. Same can be done in Go
// with function literals that accept arguments.
func sentenceFactory(mystring string) func(before, after string) string {
- return func(before, after string) string {
- return fmt.Sprintf("%s %s %s", before, mystring, after) // new string
- }
+ return func(before, after string) string {
+ return fmt.Sprintf("%s %s %s", before, mystring, after) // new string
+ }
}
func learnDefer() (ok bool) {
- // Deferred statements are executed just before the function returns.
- defer fmt.Println("deferred statements execute in reverse (LIFO) order.")
- defer fmt.Println("\nThis line is being printed first because")
- // Defer is commonly used to close a file, so the function closing the file
- // stays close to the function opening the file
- return true
+ // Deferred statements are executed just before the function returns.
+ defer fmt.Println("deferred statements execute in reverse (LIFO) order.")
+ defer fmt.Println("\nThis line is being printed first because")
+ // Defer is commonly used to close a file, so the function closing the
+ // file stays close to the function opening the file.
+ return true
}
// Define Stringer as an interface type with one method, String.
type Stringer interface {
- String() string
+ String() string
}
// Define pair as a struct with two fields, ints named x and y.
type pair struct {
- x, y int
+ x, y int
}
// 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.
- return fmt.Sprintf("(%d, %d)", p.x, p.y)
+ // Sprintf is another public function in package fmt.
+ // Dot syntax references fields of p.
+ return fmt.Sprintf("(%d, %d)", p.x, p.y)
}
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
- // Call String method of i, of type Stringer. Output same as above.
- fmt.Println(i.String())
+ // 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.
+ 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.
+ // 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.
- learnVariadicParams("great", "learning", "here!")
+ learnVariadicParams("great", "learning", "here!")
}
// Functions can have variadic parameters.
func learnVariadicParams(myStrings ...interface{}) {
- // Iterate each value of the variadic.
- // The underbar here is ignoring the index argument of the array.
- for _, param := range myStrings {
- fmt.Println("param:", param)
- }
+ // Iterate each value of the variadic.
+ // The underbar here is ignoring the index argument of the array.
+ for _, param := range myStrings {
+ fmt.Println("param:", param)
+ }
- // Pass variadic value as a variadic parameter.
- fmt.Println("params:", fmt.Sprintln(myStrings...))
+ // Pass variadic value as a variadic parameter.
+ fmt.Println("params:", fmt.Sprintln(myStrings...))
- learnErrorHandling()
+ learnErrorHandling()
}
func learnErrorHandling() {
- // ", ok" idiom used to tell if something worked or not.
- m := map[int]string{3: "three", 4: "four"}
- if x, ok := m[1]; !ok { // ok will be false because 1 is not in the map.
- fmt.Println("no one there")
- } else {
- fmt.Print(x) // x would be the value, if it were in the map.
- }
- // 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'
- fmt.Println(err)
- }
- // We'll revisit interfaces a little later. Meanwhile,
- learnConcurrency()
+ // ", ok" idiom used to tell if something worked or not.
+ m := map[int]string{3: "three", 4: "four"}
+ if x, ok := m[1]; !ok { // ok will be false because 1 is not in the map.
+ fmt.Println("no one there")
+ } else {
+ fmt.Print(x) // x would be the value, if it were in the map.
+ }
+ // 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'
+ fmt.Println(err)
+ }
+ // We'll revisit interfaces a little later. Meanwhile,
+ learnConcurrency()
}
// c is a channel, a concurrency-safe communication object.
func inc(i int, c chan int) {
- c <- i + 1 // <- is the "send" operator when a channel appears on the left.
+ c <- i + 1 // <- is the "send" operator when a channel appears on the left.
}
// We'll use inc to increment some numbers concurrently.
func learnConcurrency() {
- // 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
- // concurrently, perhaps in parallel if the machine is capable and
- // 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)
- // Read three results from the channel and print them out.
- // There is no telling in what order the results will arrive!
- fmt.Println(<-c, <-c, <-c) // channel on right, <- is "receive" operator.
+ // 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
+ // concurrently, perhaps in parallel if the machine is capable and
+ // 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)
+ // Read three results from the channel and print them out.
+ // 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.
- 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,
- fmt.Printf("it's a %T", i)
- case <-cs: // or the value received can be discarded.
- fmt.Println("it's a string")
- 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
- // goroutines started above has completed, the other will remain blocked.
+ 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,
+ fmt.Printf("it's a %T", i)
+ case <-cs: // or the value received can be discarded.
+ fmt.Println("it's a string")
+ 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
+ // goroutines started above has completed, the other will remain blocked.
- learnWebProgramming() // Go does it. You want to do it too.
+ learnWebProgramming() // Go does it. You want to do it too.
}
// A single function from package http starts a web server.
func learnWebProgramming() {
- // First parameter of ListenAndServe is TCP address to listen to.
- // Second parameter is an interface, specifically http.Handler.
- go func() {
- err := http.ListenAndServe(":8080", pair{})
- fmt.Println(err) // don't ignore errors
- }()
+ // First parameter of ListenAndServe is TCP address to listen to.
+ // Second parameter is an interface, specifically http.Handler.
+ go func() {
+ err := http.ListenAndServe(":8080", pair{})
+ fmt.Println(err) // don't ignore errors
+ }()
- requestServer();
+ requestServer()
}
-
// 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.
- w.Write([]byte("You learned Go in Y minutes!"))
+ // Serve data with a method of http.ResponseWriter.
+ w.Write([]byte("You learned Go in Y minutes!"))
}
func requestServer() {
- resp, err := http.Get("http://localhost:8080")
- fmt.Println(err)
- defer resp.Body.Close()
- body, err := ioutil.ReadAll(resp.Body)
- fmt.Printf("\nWebserver said: `%s`", string(body))
+ resp, err := http.Get("http://localhost:8080")
+ fmt.Println(err)
+ defer resp.Body.Close()
+ body, err := ioutil.ReadAll(resp.Body)
+ fmt.Printf("\nWebserver said: `%s`", string(body))
}
```