This is a creation in Article, where the information may have evolved or changed. ' Label ' is an optional parameter in the ' Break ' and ' continue ' statements, and is a mandatory argument in the ' goto ' statement. ' Label ' is only valid in the function that declares it. As long as the ' Label ' is declared in the function, it is valid throughout the scope of the function. "' Gofunc Main () {FMT. PRINTLN (1) goto ENDFMT.PRINTLN (2) end:fmt. PRINTLN (3)} "(Note!) We are the ' Label ' that is defined after the goto statement. shell>./bin/sandbox13 "The scope of the reference does not include the scope of the nested function: ' ' Gofunc () {fmt. PRINTLN ("Nested function") goto end} () End: "The above code will be compiled with the ' label End not defined ' error. In addition, it will be reported: ' label End defined and not used ', because we need to ensure that only the ' label ' needs to be declared. There is no concept of block scope in ' Label '. Therefore, you cannot declare a duplicate ' label ' in a nested block scope: ' ' Gogoto xx:{x:} ' compiles the above code to indicate that ' label ' already exists. The ' Label ' identifier and other identifiers have different namespaces, so there is no conflict with variable identifiers. The following code uses ' X ' as an identifier in both ' Label ' and variable declaration: ' Gox: = 1goto xx:fmt. PRINTLN (x) ' # # break statement ' break ' is generally used to jump out of ' for ' or ' switch ' statements. You can also use ' break ' in the ' SELECT ' statement in Go. For those with the C-class programming experience, it is certain that each ' case ' statement needs to end with ' break '. In most cases, however, the program does not want to execute into the next ' case ' statement. On the contrary, in Go, if the code that needs to execute the next clause can use the ' fallthrough ' statement: ' ' switch 1 {case 1:fmt. PRINTLN (1) Case 2:fmt. PRINTLN (2)}>./bin/sandbox1switch 1 {case 1:fmt. PRINTLN (1) fallthroUghcase 2:fmt. PRINTLN (2)}>./bin/sandbox12 "> Fallthrough can only be used as the last statement of a clause. The ' break ' statement cannot span a function boundary. "'" Gofunc f () {Break}func main () {for i: = 0; i <; i++ {f ()}} "" is reported as ' break was not in a loop ' error. In general, ' break ' can be used to jump out of ' for ', ' switch ' or ' SELECT ' statements. Use ' Label ' to get ' break ' to do more things. The ' Label ' of the ' break ' statement must correspond to ' for ', ' switch ' or ' SELECT ' statements around ' break '. So the following code cannot be compiled by: "' gofirstloop:for I: = 0; I < 10; i++ {}for I: = 0; I < 10; i++ {break Firstloop} ' it will be reported ' invalid break label Firstloop '. Because the ' Label ' is not on the loop that the break corresponds to. Break can jump out of nested loops: "' goouterloop:for I: = 0; I < 10; i++ {for J: = 0, J <, J + + (FMT). Printf ("I=%v, j=%v\n", I, J) break Outerloop} "" ">./bin/sandboxi=0, j=0" If ' break ' is used as follows, it is not just to exit the ' for ' Loop: ' Goswitchstatement:switch 1 {case 1:fmt. PRINTLN (1) for I: = 0; I < 10; i++ {break switchstatement}fmt. PRINTLN (2)}fmt. PRINTLN (3) ">/bin/sandbox13" "Break" can exit and switch to the specified ' Label ' anywhere in the ' for ', ' switch ' or ' SELECT ' statement. # # Continue statement He is similar to the ' break ' statement, but will go to the next iteration rather than exitRing (used only in loops): "' outerloop:for I: = 0; I < 3; i++ {for J: = 0; J < 3; J + + {FMT. Printf ("I=%v, j=%v\n", I, J) continue outerloop}}>./bin/sandboxi=0, J=0i=1, j=0i=2, j=0 ' # # goto statement ' goto ' statement allows the program to switch to a Continue execution where the label is labeled. "I: = 0start:fmt." PRINTLN (i) if I > 2 {goto End} else {i + = 1goto start}end: ' ' (Note: ' End ' can be null) differs from ' break ' and ' continue ' statements, ' goto ' statement must specify ' L Abel '. ' Goto ' can only move the program to a location in the same function. So there are two more rules to perform goto:-cannot skip variable declaration, if Goto skips, the compiler will report ' Goto done jumps over declaration of V at ... ' gogoto Donev: = 0done:fmt . Println (v) '-' goto ' cannot switch to another block of code, and if switched, the compiler will report ' Goto block jumps into the block starting at ... ': ' gogoto block{block:v: = 0fmt. Println (v)} "
via:https://medium.com/golangspec/labels-in-go-4ffd81932339
Author: Michałłowicki Translator: Saberuster proofreading: polaris1119
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