`FnOverload.getInstance()` design limitation

[XuechunHHH]

Description

The current implementation of FnOverloadImpl.getInstance(PType[] args) in FnOverload.java ignores the provided argument types and always returns the same function instance. This is a design limitation of the current architecture and not a simple bug.

Current Behavior

@Nullable
@Override
public Fn getInstance(PType[] args) {
    return instance; // Always returns the same instance, ignoring args
}

The FnOverload.Builder creates a single Fn instance with fixed parameter types, and FnOverloadImpl stores this single instance. The getInstance() method cannot validate argument types because it only has one pre-built instance for specific types and changing this behavior would break existing code that relies on the current implementation.

• Function overload resolution must be handled at a higher level (catalog/registry)
• The method signature suggests type validation but doesn't perform it

Additional Context

• PartiQL version: v1.2.2