Explain the use of Go's variable shadowing and redeclaration in nested scopes?
In Go, variable shadowing occurs when a variable with the same name as an outer-scoped variable is declared in an inner scope, effectively "hiding" the outer-scoped variable within that inner scope. This can be useful in cases where you need to temporarily modify the value of a variable without affecting the outer scope.
For example, consider the following code:
package main
import "fmt"
func main() {
x := 10
fmt.Println(x) // prints 10
if x := 5; x < 20 {
fmt.Println(x) // prints 5
}
fmt.Println(x) // prints 10
}
In this example, we declare a variable **x**
with the value 10 in the outer scope, and then declare another variable **x**
with the value 5 in the inner scope of the **if**
statement. This inner-scoped variable **x**
"shadows" the outer-scoped variable **x**
within the **if**
statement, so when we print the value of **x**
within the **if**
statement, we get 5 instead of 10. However, once we exit the **if**
statement and return to the outer scope, the outer-scoped variable **x**
is once again in scope and its value of 10 is printed.
Redeclaration, on the other hand, occurs when a variable with the same name is declared multiple times in the same scope. This is not allowed in Go, and will result in a compilation error. However, if the redeclaration occurs in nested scopes, it is allowed as long as each declaration is in a separate scope. For example:
package main
import "fmt"
func main() {
x := 10
fmt.Println(x) // prints 10
if y := 5; x < 20 {
fmt.Println(x, y) // prints 10 5
x := 20
fmt.Println(x, y) // prints 20 5
}
fmt.Println(x) // prints 10
}
In this example, we declare the variable **x**
with the value 10 in the outer scope, and then declare the variable **y**
with the value 5 in the inner scope of the **if**
statement. We then redeclare the variable **x**
with the value 20 in the inner scope, which is allowed because it is in a separate scope from the outer-scoped **x**
variable. When we print the values of **x**
and **y**
within the **if**
statement, we get 10 and 5 respectively, because the inner-scoped **x**
has not yet been initialized. Once we initialize the inner-scoped **x**
to 20, we print the values of **x**
and **y**
again and get 20 and 5 respectively. Finally, we print the value of the outer-scoped **x**
and get 10.