Prior to this, there have been a lot of slice in Golang, such as * [Go slices:usage and Internals] (https://blog.golang.org/ go-slices-usage-and-internals) * [How to avoid Go Gotchas] (https://blog.golang.org/go-slices-usage-and-internals) This article focuses only on the representations of slice, which can create two types of values: * truncated string* pointer to an array or slice the go language has two representations of slice: a shorthand and a complete expression. # # # abbreviated expression slice the shorthand expression is: ' ' goinput[low:high] ' where low and high are indexes of slice, whose values must be integers, which specify the input operand Which elements can be placed in the slice of the result. The input operand can be a string,array, or a pointer to an array or slice. As a result, the length of slice is high-low. The following example shows: "' gonumbers: = [10]int{0,1,2,3,4,5,6,7,8,9}s: = Numbers[2:4:6]fmt. PRINTLN (s)//[2, 3]fmt. Println (Cap (s))//4 "Applies the slice expression to the pointer to the array, which is the first time to cancel a reference to the pointer and then apply the slice expression in a general manner. A pointer to a slice expression applied to an array is a shorthand for referencing the pointer and then applying the slice expression in the usual way. "' Gonumbers: = [5]int{1, 2, 3, 4, 5}fmt. Println ((&numbers) [1:3])//[2, 3] ' Slice index low and high can be omitted, the default value of low is 0,high the length of the default value of Slice: ' ' gofmt. Println ("foo" [: 2])//"fo" FMT. Println ("foo" [1:])//"oo" FMT. Println ("foo" [:])//"foo", but Slice's index cannot be any of the following types of values: *Low < 0 or High < 0* low <= high* high <= len (input) ' gofmt. Println ("foo" [-1:])//Invalid slice index-1 (index must be non-negative)//fmt. Println ("foo" [: 4])//Invalid slice index 4 (out of the bounds for 3-byte string) fmt. Println ("foo" [2:2])//"" (blank)//fmt. Println ("foo" [2:1])//Invalid slice index:2 > 1 ' "Otherwise, even if an index over the slice range cannot be detected at compile time, a panic will occur at run time. "' Gofunc low () int {return 4}func main () {FMT. Println ("foo" [Low ():])} "" Panic:runtime error:slice bounds out of Rangegoroutine 1 [running]:p anic (0x102280, 0x1040a018)/usr/local/go/src/runtime/panic.go:500 +0x720main.main ()/tmp/sandbox685025974/main.go:12 +0x120 "# # Complete expression This method controls the capacity of the result slice, but only for arrays and pointers to arrays or slice (string is not supported), and the capacity of the result slice in a shorthand expression is the maximum possible capacity starting at index low (a shorthand representation of slice Gonumbers: = [10]int{0,1,2,3,4,5,6,7,8,9}s: = Numbers[1:4]fmt. PRINTLN (s)//[1, 2, 3]fmt. Println (Cap (s))//9 "for an array, cap (a) = = Len (a) in the preceding code fragment, the capacity of S is 9 because the slice starts at index 1, and the underlying array has 8 elements (2 to 9). Complete expression of sliceAllows you to modify this default behavior, as in the following code: "Gonumbers: = [10]int{0,1,2,3,4,5,6,7,8,9}s: = Numbers[1:4:5]fmt. PRINTLN (s)//[1, 2, 3]fmt. Println (Cap (s))//4 "' complete slice expression has the following form: ' ' Goinput[low:high:max ' ' Index low and index high are the same meaning and work as a shorthand expression. The only difference is that Max sets the capacity of the result slice to Max-low. "' Gonumbers: = [10]int{0,1,2,3,4,5,6,7,8,9}s: = Numbers[2:4:6]fmt. PRINTLN (s)//[2, 3]fmt. Println (Cap (s))//4 "When the input operand of the slice is a slice, the capacity of the resulting slice depends on the input operand, not the underlying array it points to:" ' gonumbers: = [10]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}fmt. Println (Cap (numbers))//10S1: = numbers[1:4]fmt. PRINTLN (S1)//[1, 2, 3]fmt. Println (Cap (S1))//9S2: = numbers[1:4:5]fmt. PRINTLN (S2)//[1, 2, 3]fmt. Println (Cap (S2))//4S3: = s2[:]fmt. PRINTLN (S3)//[1, 2, 3]fmt. PRINTLN (S3)//4 "In this example, the capacity of S3 cannot exceed the capacity of S2 (4), even if the array it points to has 10 elements, and S1,S2,S3 starts at 1. When the input operand is slice, the full expression's index high cannot exceed its cap (input) ' gonumbers: = [10]INT{0,1,2,3,4,5,6,7,8,9}S1: = Numbers[0:1]fmt. PRINTLN (S1)//[0]FMT. Println (len (S1))//1FMT. Println (Cap (S1))//10S2: = NUMBERS[0:5]FMT.PRINTLN (S2)//[0, 1, 2, 3, 4]fmt. Println (Cap (S1))//10 "In addition, for its max value, there are two additional rules * High <= max* max <= Cap (input) ' gonumbers: = [10]int{0,1,2,3,4,5, 6,7,8,9}S1: = numbers[0:1]s2: = numbers[0:5:11]//Invalid slice index One (out of the bounds for 10-element array) fmt. Println (S1, S2) "In a complete slice expression The low index is" gonumbers ": = [10]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}s: = numbers[:4:6]fmt. PRINTLN (s)//[0, 1, 2, 3]fmt. Println (Cap (s))//6 ", however, can not omit a slightly higher index (high) ' gonumbers: = [10]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}s1: = numbers[:4:6]s2: = s1[: : 5]fmt. PRINTLN (S2) fmt. Println (Cap (S2)) "Otherwise, the code will be in the Compile Times Error" Middle index required in 3-index slice "
via:https://medium.com/golangspec/slice-expressions-in-go-963368c20765
Author: Michałłowicki Translator: Bizky proofreading: polaris1119
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