Does Go\'s Embedding Approach Eliminate the Fragile Base Class Issue?

Fragile Base Class Issue in Go: A Subtle Difference

Despite embracing composition over inheritance as a design principle, the question lingers: does the fragile base class issue exist in Go?

Defining the Fragile Base Class Issue

The fragile base class problem arises when a change in the base class affects its derived classes in unintended ways. This occurs due to polymorphism, where methods in derived classes can override those in the base class. If the base class method is then modified, it can unintentionally break the behavior of the derived classes.

Go's Perspective on the Issue

In Go, polymorphism is absent due to the lack of virtual methods. Instead, Go utilizes embedding, where a struct can contain another struct and directly access its methods. While this approach eliminates the direct impact of the fragile base class issue, it introduces a subtle nuance.

Embedding and Method Promotion

When a struct is embedded, all its methods are promoted to the enclosing struct. However, these methods cannot be overridden in the enclosing struct. Instead, new methods with the same name can be added, but calling the promoted method from within the embedded struct will still invoke the original definition.

An Example in Context

Let's consider the following Java example that demonstrates the fragile base class issue:

<code class="java">class Counter {
    int value;
    void inc() { value++; }
    void incBy(int n) { value += n; }
}
class MyCounter extends Counter {
    @Override
    void inc() { incBy(1); }
}</code>

Here, modifying Counter.incBy() to iterate and call inc() would break MyCounter.inc(), leading to an infinite loop.

In Go, however, a similar example would not result in such a break due to the lack of polymorphism. The embedded Counter methods cannot be overridden, so the original Counter.Inc() method would always be invoked, regardless of the calling context.

<code class="go">type Counter struct {
    value int
}
func (c *Counter) Inc() { c.value++ }
func (c *Counter) IncBy(n int) { c.value += n }
type MyCounter struct {
    Counter
}
func (m *MyCounter) Inc() { m.IncBy(1) }</code>

In this case, modifying Counter.IncBy() would not affect MyCounter.Inc(), which would continue to increment the counter by 1.

Conclusion

While Go mitigates the fragile base class issue due to the absence of virtual methods, it does not eliminate it entirely. The promotion of methods during embedding introduces a nuanced form of the issue. However, this nuance is less disruptive and more predictable compared to the classic fragile base class problem.

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