Is Nested Class Functionality Available Within Functions in Go?

Nested Class Inside a Function in Go

Go allows the nesting of structs within functions for encapsulation purposes. However, the question arises: Is there a mechanism to define nested classes within functions?

In Go, nested functions are not permitted, except for lambdas. This restriction raises concerns about class functionality within functions.

To expand on this issue, the following code example illustrates the limitations:

<code class="go">func f() {
    // Nested struct Cls inside f
    type Cls struct {
        // ...
    }
    // Attempt to bind foo to Cls (fails)
    func (c *Cls) foo() {
        // ...
    }
}</code>

This code attempts to create a nested class Cls within function f, but the attempt to bind method foo to Cls fails. It appears that classes are weakened within functions.

To address this limitation, Go provides the concept of function literals. Function literals allow you to declare a function and assign it to a variable. Using this approach, you can create something similar to nested functions:

<code class="go">func f() {
    foo := func(s string) {
        fmt.Println(s)
    }

    foo("Hello World!")
}</code>

In this example, a function literal foo is created and assigned to a variable within function f. Calling f outputs "Hello World!" as expected.

While function literals provide a workaround for nesting functions, it is important to note that they are not true nested functions and have certain limitations compared to nested classes in other languages.

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