Ambiguity Errors with Generics

1. What Are Ambiguity Errors?

• Arise when erasure transforms two apparently distinct generic declarations into identical types, causing compilation conflicts.
• They are especially common in scenarios involving method overloading.

2. Example of Ambiguity: Erasure Overload

Problematic code:

class MyGenClass<T, V> {
    T ob1;
    V ob2;

    // Tentativa de sobrecarga
    void set(T o) {
        ob1 = o;
    }

    void set(V o) {
        ob2 = o;
    }
}

Error: The attempt to overload the set() method based on the generic parameters T and V appears valid, but causes ambiguity.

3. Reasons for Ambiguity

• First Problem: T and V can be the same type.

Example:

MyGenClass<String, String> obj = new MyGenClass<>();

Here, both T and V are replaced by String, making the two versions of set() identical.

Result:

• The compiler cannot distinguish between the two methods.

Second Problem: Erasure reduces types to Object.

• During compilation, both methods are transformed into:

void set(Object o) {
    // ...
}

This eliminates any distinction between T and V, making overloading impossible.

4. Why Does This Happen?

• Erasure removes generic type information, replacing it with its boundary types (or Object if no boundary is specified).
• In the case of set(T) and set(V), both end up being treated as set(Object) in the code generated by the compiler.

5. Solution: Avoid Generic Overload
To resolve the ambiguity, use different names for the methods.

Corrected example:

class MyGenClass<T, V> {
    T ob1;
    V ob2;

    void setOb1(T o) {
        ob1 = o;
    }

    void setOb2(V o) {
        ob2 = o;
    }
}

Here, setOb1() and setOb2() are distinct methods, eliminating the conflict.

6. Conclusion
Ambiguities like this occur because erasure transforms generic parameters into simple types (Object).
To avoid mistakes, follow these practices:

• Avoid overloading methods with generic parameters.
• Give different names to methods that manipulate different generic types. Understanding erasure behavior helps prevent these problems and design generic classes safely.

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