mirror of
https://github.com/adambard/learnxinyminutes-docs.git
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Merge pull request #676 from heyalexej/patch-1
fix import of io/ioutil, run gofmt
This commit is contained in:
Levi Bostian
commit
57c384420e
437
go.html.markdown
437
go.html.markdown
@ -9,6 +9,7 @@ contributors:
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- ["Jesse Johnson", "https://github.com/holocronweaver"]
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- ["Quint Guvernator", "https://github.com/qguv"]
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- ["Jose Donizetti", "https://github.com/josedonizetti"]
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- ["Alexej Friesen", "https://github.com/heyalexej"]
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---
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Go was created out of the need to get work done. It's not the latest trend
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@ -33,87 +34,88 @@ package main
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// Import declaration declares library packages referenced in this file.
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import (
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"fmt" // A package in the Go standard library.
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"net/http" // Yes, a web server!
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"strconv" // String conversions.
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m "math" // Math library with local alias m.
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"fmt" // A package in the Go standard library.
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"io/ioutil" // Implements some I/O utility functions.
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m "math" // Math library with local alias m.
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"net/http" // Yes, a web server!
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"strconv" // String conversions.
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)
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// A function definition. Main is special. It is the entry point for the
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// executable program. Love it or hate it, Go uses brace brackets.
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func main() {
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// Println outputs a line to stdout.
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// Qualify it with the package name, fmt.
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fmt.Println("Hello world!")
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// Println outputs a line to stdout.
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// Qualify it with the package name, fmt.
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fmt.Println("Hello world!")
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// Call another function within this package.
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beyondHello()
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// Call another function within this package.
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beyondHello()
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}
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// Functions have parameters in parentheses.
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// If there are no parameters, empty parentheses are still required.
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func beyondHello() {
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var x int // Variable declaration. Variables must be declared before use.
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x = 3 // Variable assignment.
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// "Short" declarations use := to infer the type, declare, and assign.
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y := 4
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sum, prod := learnMultiple(x, y) // Function returns two values.
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fmt.Println("sum:", sum, "prod:", prod) // Simple output.
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learnTypes() // < y minutes, learn more!
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var x int // Variable declaration. Variables must be declared before use.
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x = 3 // Variable assignment.
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// "Short" declarations use := to infer the type, declare, and assign.
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y := 4
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sum, prod := learnMultiple(x, y) // Function returns two values.
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fmt.Println("sum:", sum, "prod:", prod) // Simple output.
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learnTypes() // < y minutes, learn more!
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}
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// Functions can have parameters and (multiple!) return values.
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func learnMultiple(x, y int) (sum, prod int) {
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return x + y, x * y // Return two values.
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return x + y, x * y // Return two values.
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}
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// Some built-in types and literals.
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func learnTypes() {
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// Short declaration usually gives you what you want.
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s := "Learn Go!" // string type.
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// Short declaration usually gives you what you want.
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s := "Learn Go!" // string type.
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s2 := `A "raw" string literal
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s2 := `A "raw" string literal
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can include line breaks.` // Same string type.
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// Non-ASCII literal. Go source is UTF-8.
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g := 'Σ' // rune type, an alias for uint32, holds a unicode code point.
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// Non-ASCII literal. Go source is UTF-8.
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g := 'Σ' // rune type, an alias for uint32, holds a unicode code point.
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f := 3.14195 // float64, an IEEE-754 64-bit floating point number.
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c := 3 + 4i // complex128, represented internally with two float64's.
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f := 3.14195 // float64, an IEEE-754 64-bit floating point number.
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c := 3 + 4i // complex128, represented internally with two float64's.
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// Var syntax with an initializers.
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var u uint = 7 // Unsigned, but implementation dependent size as with int.
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var pi float32 = 22. / 7
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// Var syntax with an initializers.
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var u uint = 7 // Unsigned, but implementation dependent size as with int.
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var pi float32 = 22. / 7
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// Conversion syntax with a short declaration.
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n := byte('\n') // byte is an alias for uint8.
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// Conversion syntax with a short declaration.
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n := byte('\n') // byte is an alias for uint8.
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// Arrays have size fixed at compile time.
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var a4 [4]int // An array of 4 ints, initialized to all 0.
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a3 := [...]int{3, 1, 5} // An array of 3 ints, initialized as shown.
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// Arrays have size fixed at compile time.
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var a4 [4]int // An array of 4 ints, initialized to all 0.
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a3 := [...]int{3, 1, 5} // An array of 3 ints, initialized as shown.
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// Slices have dynamic size. Arrays and slices each have advantages
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// but use cases for slices are much more common.
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s3 := []int{4, 5, 9} // Compare to a3. No ellipsis here.
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s4 := make([]int, 4) // Allocates slice of 4 ints, initialized to all 0.
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var d2 [][]float64 // Declaration only, nothing allocated here.
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bs := []byte("a slice") // Type conversion syntax.
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// Slices have dynamic size. Arrays and slices each have advantages
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// but use cases for slices are much more common.
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s3 := []int{4, 5, 9} // Compare to a3. No ellipsis here.
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s4 := make([]int, 4) // Allocates slice of 4 ints, initialized to all 0.
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var d2 [][]float64 // Declaration only, nothing allocated here.
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bs := []byte("a slice") // Type conversion syntax.
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p, q := learnMemory() // Declares p, q to be type pointer to int.
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fmt.Println(*p, *q) // * follows a pointer. This prints two ints.
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p, q := learnMemory() // Declares p, q to be type pointer to int.
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fmt.Println(*p, *q) // * follows a pointer. This prints two ints.
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// Maps are a dynamically growable associative array type, like the
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// hash or dictionary types of some other languages.
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m := map[string]int{"three": 3, "four": 4}
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m["one"] = 1
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// Maps are a dynamically growable associative array type, like the
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// hash or dictionary types of some other languages.
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m := map[string]int{"three": 3, "four": 4}
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m["one"] = 1
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// Unused variables are an error in Go.
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// The underbar lets you "use" a variable but discard its value.
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_, _, _, _, _, _, _, _, _ = s2, g, f, u, pi, n, a3, s4, bs
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// Output of course counts as using a variable.
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fmt.Println(s, c, a4, s3, d2, m)
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// Unused variables are an error in Go.
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// The underbar lets you "use" a variable but discard its value.
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_, _, _, _, _, _, _, _, _ = s2, g, f, u, pi, n, a3, s4, bs
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// Output of course counts as using a variable.
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fmt.Println(s, c, a4, s3, d2, m)
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learnFlowControl() // Back in the flow.
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learnFlowControl() // Back in the flow.
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}
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// It is possible, unlike in many other languages for functions in go
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@ -122,250 +124,249 @@ can include line breaks.` // Same string type.
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// allows us to easily return from multiple points in a function as well as to
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// only use the return keyword, without anything further.
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func learnNamedReturns(x, y int) (z int) {
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z = x * y
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return // z is implicit here, because we named it earlier.
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z = x * y
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return // z is implicit here, because we named it earlier.
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}
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// Go is fully garbage collected. It has pointers but no pointer arithmetic.
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// You can make a mistake with a nil pointer, but not by incrementing a pointer.
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func learnMemory() (p, q *int) {
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// Named return values p and q have type pointer to int.
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p = new(int) // Built-in function new allocates memory.
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// The allocated int is initialized to 0, p is no longer nil.
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s := make([]int, 20) // Allocate 20 ints as a single block of memory.
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s[3] = 7 // Assign one of them.
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r := -2 // Declare another local variable.
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return &s[3], &r // & takes the address of an object.
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// Named return values p and q have type pointer to int.
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p = new(int) // Built-in function new allocates memory.
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// The allocated int is initialized to 0, p is no longer nil.
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s := make([]int, 20) // Allocate 20 ints as a single block of memory.
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s[3] = 7 // Assign one of them.
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r := -2 // Declare another local variable.
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return &s[3], &r // & takes the address of an object.
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}
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func expensiveComputation() float64 {
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return m.Exp(10)
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return m.Exp(10)
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}
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func learnFlowControl() {
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// If statements require brace brackets, and do not require parens.
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if true {
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fmt.Println("told ya")
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}
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// Formatting is standardized by the command line command "go fmt."
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if false {
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// Pout.
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} else {
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// Gloat.
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}
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// Use switch in preference to chained if statements.
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x := 42.0
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switch x {
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case 0:
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case 1:
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case 42:
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// Cases don't "fall through".
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case 43:
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// Unreached.
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}
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// Like if, for doesn't use parens either.
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// Variables declared in for and if are local to their scope.
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for x := 0; x < 3; x++ { // ++ is a statement.
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fmt.Println("iteration", x)
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}
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// x == 42 here.
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// If statements require brace brackets, and do not require parens.
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if true {
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fmt.Println("told ya")
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}
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// Formatting is standardized by the command line command "go fmt."
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if false {
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// Pout.
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} else {
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// Gloat.
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}
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// Use switch in preference to chained if statements.
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x := 42.0
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switch x {
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case 0:
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case 1:
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case 42:
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// Cases don't "fall through".
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case 43:
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// Unreached.
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}
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// Like if, for doesn't use parens either.
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// Variables declared in for and if are local to their scope.
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for x := 0; x < 3; x++ { // ++ is a statement.
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fmt.Println("iteration", x)
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}
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// x == 42 here.
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// For is the only loop statement in Go, but it has alternate forms.
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for { // Infinite loop.
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break // Just kidding.
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continue // Unreached.
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}
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// As with for, := in an if statement means to declare and assign y first,
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// then test y > x.
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if y := expensiveComputation(); y > x {
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x = y
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}
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// Function literals are closures.
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xBig := func() bool {
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return x > 10000 // References x declared above switch statement.
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}
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fmt.Println("xBig:", xBig()) // true (we last assigned e^10 to x).
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x = 1.3e3 // This makes x == 1300
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fmt.Println("xBig:", xBig()) // false now.
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// For is the only loop statement in Go, but it has alternate forms.
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for { // Infinite loop.
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break // Just kidding.
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continue // Unreached.
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}
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// As with for, := in an if statement means to declare and assign
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// y first, then test y > x.
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if y := expensiveComputation(); y > x {
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x = y
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}
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// Function literals are closures.
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xBig := func() bool {
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return x > 10000 // References x declared above switch statement.
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}
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fmt.Println("xBig:", xBig()) // true (we last assigned e^10 to x).
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x = 1.3e3 // This makes x == 1300
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fmt.Println("xBig:", xBig()) // false now.
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|
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// What's more is function literals may be defined and called inline,
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// acting as an argument to function, as long as:
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// a) function literal is called immediately (),
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// b) result type matches expected type of argument.
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fmt.Println("Add + double two numbers: ",
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func(a, b int) int {
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return (a + b) * 2
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}(10, 2)) // Called with args 10 and 2
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// => Add + double two numbers: 24
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|
||||
// When you need it, you'll love it.
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goto love
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// What's more is function literals may be defined and called inline,
|
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// acting as an argument to function, as long as:
|
||||
// a) function literal is called immediately (),
|
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// b) result type matches expected type of argument.
|
||||
fmt.Println("Add + double two numbers: ",
|
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func(a, b int) int {
|
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return (a + b) * 2
|
||||
}(10, 2)) // Called with args 10 and 2
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// => Add + double two numbers: 24
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|
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// When you need it, you'll love it.
|
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goto love
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love:
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learnFunctionFactory() // func returning func is fun(3)(3)
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learnDefer() // A quick detour to an important keyword.
|
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learnInterfaces() // Good stuff coming up!
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learnFunctionFactory() // func returning func is fun(3)(3)
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learnDefer() // A quick detour to an important keyword.
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learnInterfaces() // Good stuff coming up!
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}
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func learnFunctionFactory() {
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// Next two are equivalent, with second being more practical
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fmt.Println(sentenceFactory("summer")("A beautiful", "day!"))
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// Next two are equivalent, with second being more practical
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fmt.Println(sentenceFactory("summer")("A beautiful", "day!"))
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d := sentenceFactory("summer")
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fmt.Println(d("A beautiful", "day!"))
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fmt.Println(d("A lazy", "afternoon!"))
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d := sentenceFactory("summer")
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fmt.Println(d("A beautiful", "day!"))
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fmt.Println(d("A lazy", "afternoon!"))
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}
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|
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// Decorators are common in other languages. Same can be done in Go
|
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// with function literals that accept arguments.
|
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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 {
|
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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))
|
||||
}
|
||||
```
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user