The following tutorial column will share with you the pitfalls of Go’s loop traversal, I hope it will be helpful to friends who need it!
In Golang's flow control, there are two types of loop statements: for and range.
for statement
1.for assignment expression; relational expression or logical expression; assignment expression{}
for i := 0; i <p><code>2.for relational expression or logical expression { }</code></p><pre class="brush:php;toolbar:false">n := 10for n > 0 { n--}
3.for { }
for { fmt.Println("hello world") } // 等价于 // for true { // fmt.Println("hello world") // }
range statementGolang range is similar to the iterator operation and can iterate over slices, maps, arrays, strings, etc. It returns (index, value) in strings, arrays, and slices, and (key, value) in collections, but when there is only one return value, the first argument is the index or key.
str := "abc" for i, char := range str { fmt.Printf("%d => %s\n", i, string(char)) } for i := range str { //只有一个返回值 fmt.Printf("%d\n", i) } nums := []int{1, 2, 3} for i, num := range nums { fmt.Printf("%d => %d\n", i, num) } kvs := map[string]string{"a": "apple", "b": "banana"} for k, v := range kvs { fmt.Printf("%s => %s\n", k, v) } for k := range kvs { //只有一个返回值 fmt.Printf("%s\n", k) } // 输出结果 // 0 => a // 1 => b // 2 => c // 0 // 1 // 2 // 0 => 1 // 1 => 2 // 2 => 3 // a => apple // b => banana // a // b
The for loop, especially the range statement, is frequently used in the normal development process, but many developers (I am one of them) often make mistakes in the following scenarios.
Scenario 1, using the variables of the loop iterator
Let’s look at an obvious mistake first: func main() {
var out []*int
for i := 0; i < 3; i++ {
// i := i
out = append(out, &i)
}
fmt.Println("值:", *out[0], *out[1], *out[2])
fmt.Println("地址:", out[0], out[1], out[2])
}
// 输出结果
// 值: 3 3 3
// 地址: 0xc000012090 0xc000012090 0xc000012090
Analysisiout
is an integer pointer array variable. In the for loop, a
variable is declared, and the address of i
is stored in each loop. Append to the out
slice, but each append is actually the i
variable, so what we append is the same address, and the final value of the address is 3. Correct approach
Unlock the comments in the codeVariables.// i := i
, create a new # each time through the loop ##i
Let’s look at a more subtle mistake:
<pre class='brush:php;toolbar:false;'>func main() {
a1 := []int{1, 2, 3}
a2 := make([]*int, len(a1))
for i, v := range a1 {
a2[i] = &v
}
fmt.Println("值:", *a2[0], *a2[1], *a2[2])
fmt.Println("地址:", a2[0], a2[1], a2[2])
}
// 输出结果
// 值: 3 3 3
// 地址: 0xc000012090 0xc000012090 0xc000012090</pre>
Most people are here
rangeis traversing the value type,This is a pitfall when assigning values to variables because it is relatively secretive. In fact, the situation is the same as above. When
range
v is a local variable and will only be initialized. Once, and then reassign the previous one every time it loops, so when assigning a value to
a2[i], it is actually the same address
&v, and
v The final value is the value of the last element of
a1, which is 3.
Correct approach
a2[i]Pass the original pointer when assigning, that is,
a2[i] = &a1[i]
②Create temporary variablet := v
;a2[i] = &t
③Closure (same principle as ②), func (v int) { a2[i] = &v }(v)
The more secretive thing is: <pre class="brush:php;toolbar:false">func main() {
var out [][]int
for _, i := range [][1]int{{1}, {2}, {3}} {
out = append(out, i[:])
}
fmt.Println("Values:", out)}// 输出结果// [[3] [3] [3]]</pre>
The principle is the same, no matter how many times it is traversed ,
is always overwritten by the value of this traversal
Scenario 2, using goroutines in the loop body
func main() { values := []int{1, 2, 3} wg := sync.WaitGroup{} for _, val := range values { wg.Add(1) go func() { fmt.Println(val) wg.Done() }() } wg.Wait()}// 输出结果// 3// 3// 3
Analysis
For the main coroutine, the loop is completed quickly, and each coroutine may only start running at this time. At this time, the value ofval. (If the traversal data is huge and the main coroutine traversal takes a long time, the output of the goroutine will be based on the value ofhas already The traversal has reached the last one, so each coroutine outputs
3
val at that time, so the output result is not necessarily the same each time.)
Solution
for _, val := range values { wg.Add(1) val := val go func() { fmt.Println(val) wg.Done() }()}②Use closure
for _, val := range values { wg.Add(1) go func(val int) { fmt.Println(val) wg.Done() }(val)}
The above is the detailed content of Record the pitfalls of Go's loop traversal. For more information, please follow other related articles on the PHP Chinese website!

Effective Go application error logging requires balancing details and performance. 1) Using standard log packages is simple but lacks context. 2) logrus provides structured logs and custom fields. 3) Zap combines performance and structured logs, but requires more settings. A complete error logging system should include error enrichment, log level, centralized logging, performance considerations, and error handling modes.

EmptyinterfacesinGoareinterfaceswithnomethods,representinganyvalue,andshouldbeusedwhenhandlingunknowndatatypes.1)Theyofferflexibilityforgenericdataprocessing,asseeninthefmtpackage.2)Usethemcautiouslyduetopotentiallossoftypesafetyandperformanceissues,

Go'sconcurrencymodelisuniqueduetoitsuseofgoroutinesandchannels,offeringalightweightandefficientapproachcomparedtothread-basedmodelsinlanguageslikeJava,Python,andRust.1)Go'sgoroutinesaremanagedbytheruntime,allowingthousandstorunconcurrentlywithminimal

Go'sconcurrencymodelusesgoroutinesandchannelstomanageconcurrentprogrammingeffectively.1)Goroutinesarelightweightthreadsthatalloweasyparallelizationoftasks,enhancingperformance.2)Channelsfacilitatesafedataexchangebetweengoroutines,crucialforsynchroniz

InterfacesandpolymorphisminGoenhancecodereusabilityandmaintainability.1)Defineinterfacesattherightabstractionlevel.2)Useinterfacesfordependencyinjection.3)Profilecodetomanageperformanceimpacts.

TheinitfunctioninGorunsautomaticallybeforethemainfunctiontoinitializepackagesandsetuptheenvironment.It'susefulforsettingupglobalvariables,resources,andperformingone-timesetuptasksacrossanypackage.Here'showitworks:1)Itcanbeusedinanypackage,notjusttheo

Interface combinations build complex abstractions in Go programming by breaking down functions into small, focused interfaces. 1) Define Reader, Writer and Closer interfaces. 2) Create complex types such as File and NetworkStream by combining these interfaces. 3) Use ProcessData function to show how to handle these combined interfaces. This approach enhances code flexibility, testability, and reusability, but care should be taken to avoid excessive fragmentation and combinatorial complexity.

InitfunctionsinGoareautomaticallycalledbeforethemainfunctionandareusefulforsetupbutcomewithchallenges.1)Executionorder:Multipleinitfunctionsrunindefinitionorder,whichcancauseissuesiftheydependoneachother.2)Testing:Initfunctionsmayinterferewithtests,b


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment

EditPlus Chinese cracked version
Small size, syntax highlighting, does not support code prompt function

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

Atom editor mac version download
The most popular open source editor

WebStorm Mac version
Useful JavaScript development tools
