The Dual Pillars, Purity & Encapsulation - Part1

> written with improvements and the help of Deepseek

#### The Illusion of Separation

Purity (functional) and encapsulation (OOP) appear orthogonal, one born of mathematical ideals, the other of object-oriented paradigm. Yet both are existential responses to chaos: _the entropy of state_. Purity constrains mutation; encapsulation cages it. Their dialectic reveals a shared mandate: **control over side effects** as the foundation of reason.

#### Purity: The Functional Imperative

A pure function is a closed system:

- **No side effects** (immutable interactions).

- **Referential transparency** (output solely determined by inputs).

```

const square = n => n * n;

// Impure: Leaks side effects

let count = 0;

const increment = () => ++count; // Mutates external state

```

_Purity mirrors [Leibniz’s identity of indiscernibles](https://plato.stanford.edu/entries/identity-indiscernible/) where identical inputs must yield identical outputs. Violations fracture determinism_

#### Encapsulation: OOP’s State Monad

Encapsulation binds state and behavior, exposing only _intended_ mutations. It is purity’s object-oriented shadow:

- **State is internalized** (hidden from direct access).

- **Mutators are curated** (methods enforce invariants).

```

class Counter {

_count = 0; // Encapsulated state

increment() {

this._count++; // Controlled mutation

}

get value() { return this._count; }

}

const counter = new Counter();

counter.increment(); // State change is intentional & contained

```

_Similar to [Kant’s _noumenon_](https://en.wikipedia.org/wiki/Noumenon), encapsulated state is unknowable except through its phenomena (methods) where the universe is the (object)_

#### Simple & Shallow Comparison

|**Purity**|**Encapsulation**|

|--|--|

| Avoids state|Owns state|

|Externally stateless |Internally stateful |

|Shares via composition |Shares via messaging |

|State is a sin |State is inevitable but we can govern it|

|Eliminates implicit dependencies |Localizes dependencies |

|Manage state by scope |Manage state by access boundaries|

| excels in stateless transformations (data pipelines, concurrency)|masters stated entities (UI components, domain models)|

#### Choose Your Weapon

- **Renounce the mutation & reject impurity** --> PURE

- **Ritualize the mutation & master the impurity** --> Encapsulation