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76 lines
2.0 KiB
Go
76 lines
2.0 KiB
Go
package main
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import "fmt"
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// Sample code is taken from online tutorial https://blog.learngoprogramming.com/gotchas-of-defer-in-go-1-8d070894cb01
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// it demostrate all the common GOTCHA when using defer.
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// If a deferred func evaluates to nil, execution panic when surrounding func ends not when defer is called
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func nilFuncDefer() {
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var run func() = nil
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defer run()
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fmt.Println("runs")
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}
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// Do not use defer inside a loop unless you are sure about what you are doing. It may not work as expected.
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// However, in some situations it will be handy for instance,delegating the recursivity of a func to a defer.
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func deferInsideLoop() {
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nums := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}
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for _, v := range nums {
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defer func(v int) {
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fmt.Println(v)
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}(v)
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}
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}
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// The deferred func above will only run when the func ends not when the deferred func’s surrounding block ends
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// (the area inside curly braces containing the defer call). As seen in the example code, you can create separate blocks just using curly braces.
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func block() {
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{
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defer func() {
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fmt.Println("block: defer runs")
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}()
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}
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fmt.Println("main: ends")
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}
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type Car struct {
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model string
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}
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func (c Car) PrintModel() {
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fmt.Println(c.model)
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}
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type Dog struct {
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name string
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}
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func (d *Dog) MakeSound() {
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fmt.Println("WOFF my name is", d.name)
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}
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// So, when a method with a value-receiver is used with defer, the receiver will be copied (in this case Car) at the time of
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// registering and the changes to it wouldn’t be visible (Car.model). Because, the receiver is also an input param and evaluated immediately to “DeLorean DMC-12” when it’s
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// registered with the defer.
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func deferStruct() {
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c := Car{model: "model 1211"}
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defer c.PrintModel()
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c.model = "model 2018"
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}
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// Remember that the passed params to a deferred func are saved aside immediately without waiting the deferred func to be run.
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func deferPointer() {
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d := &Dog{name: "James"}
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defer d.MakeSound()
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d.name = "Ann"
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}
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func main() {
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// nilFuncDefer()
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// deferInsideLoop()
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// block()
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// deferStruct()
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deferPointer()
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}
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