How Can I Display the Pointer Value of a Go Object? Unraveling the Significance of Pointer Values
In Go, understanding whether structs are passed by value or reference is crucial. This article dives into this concept and explores a technique for printing the pointer value of an object in Go.
Understanding Value vs. Reference Passing
Go functions pass arguments by value, meaning that the function receives a copy of the original object. This implies that any changes made to the argument within the function do not affect the original object. Conversely, if structures are passed by reference, any changes made within the function are reflected in the original object.
Revealing Pointer Values in Go
To determine whether a struct is passed by value or reference, it's helpful to inspect its pointer value. In Go, & operator returns a pointer to the variable, which can be printed using the %p format specifier. However, this pointer value may change during garbage collection.
To obtain a persistent object ID, using the runtime.SetFinalizer() function is recommended. This involves providing a finalizer, which gets called just before the garbage collector removes the object. By creating a uniqueness map in the finalizer, you can assign a unique ID to each object to identify it throughout its lifetime.
Extending the Example
Consider the following Go code:
package main import ( "fmt" "runtime" ) type Something struct { number int queue chan int } func gotest(s *Something, done chan bool) { fmt.Println("from gotest:") fmt.Println(&s) for num := range s.queue { fmt.Println(num) s.number = num } done <- true } func main() { runtime.GOMAXPROCS(4) s := new(Something) fmt.Println(&s) s.queue = make(chan int) done := make(chan bool) go gotest(s, done) s.queue <- 42 close(s.queue) <-done fmt.Println(&s) fmt.Println(s.number) }
Running this code would output:
0x4930d4 from gotest: 0x4974d8 42 0x4930d4 42
This demonstrates that the pointer value within the go routine is different from the original object, but the value of the number field is updated correctly.
Conclusion
While Go functions pass arguments by value, you can still inspect pointer values to understand the behavior of your code. Using techniques like setting finalizers, you can gain insight into the object's identity and reference behavior, which can be especially helpful in concurrent programming scenarios.
The above is the detailed content of How Can I Display and Track the Pointer Value of a Go Object Throughout Its Lifetime?. For more information, please follow other related articles on the PHP Chinese website!