Closures vs Parameters in Go: When to Use Which for Anonymous Functions?

Parameter vs Closure: Delving into the Nuances

In Go, closures and function parameters provide distinct mechanisms for handling variables within anonymous functions. Let's delve into the nuances and explore when one approach is superior to the other.

Closures: Shared Variable Access

When an anonymous function acts as a closure, it retains access to the variables defined in the surrounding scope. These variables are shared among all instances of the closure, meaning they refer to the same memory address. This can be advantageous when you want multiple function calls to operate on the same data, such as maintaining a running total or incrementing a counter.

Function Parameter: Copying Value

In contrast, when you pass a parameter to an anonymous function, the function receives a copy of the value. This means that each instance of the function has its own distinct copy of the variable, isolated from the calling scope. This is beneficial when you want each function call to operate independently, without affecting the original value.

Choosing the Right Approach

The choice between using a closure or a function parameter depends on the intended behavior. If you need all function calls to share the same variable and its modifications, a closure is more appropriate. On the other hand, if each function call should operate on its own copy of the variable, a parameter should be employed.

To illustrate this difference, consider the following examples:

Closure:

for i := 0; i < 3; i++ {
    go func() {
        fmt.Println(i)
    }()
}

Parameter:

for i := 0; i < 3; i++ {
    go func(v int) {
        fmt.Println(v)
    }(i)
}

In the closure example, all function calls will access the same shared variable i, which has a final value of 3 when the goroutines execute. This results in the output 3 being printed three times.

In the function parameter example, however, each function call receives a copy of the variable i at the time of the call. Therefore, the output is 0, 1, and 2, as each goroutine prints the value of i at the moment it was passed as an argument.

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