Insider Trading

Symptom

Modules reach into each other's internals to coordinate behavior, bypassing public interfaces.

Goal

Cooperation happens through narrow, explicit interfaces; secrets stay secret.

Smellier version

class A { _data; }
class B {
  read(a) {
    return a._data.value;
  }
}

Fresher version

class A { value() { return this._data.value; } }
class B { read(a) { return a.value(); } }

Savings

Module boundaries become real; tests exercise the public surface; refactoring is local.

Note

Coupling at the implementation level — refactoring one breaks the other in non-obvious ways.