Eleza Kanuni ya Open/Closed Principle kwa undani.

Question

Accepted Answer

**Open/Closed Principle (OCP)** inasema kuwa huluki za programu zinapaswa kuwa **zilizofunguliwa kwa upanuzi lakini zilizofungwa kwa mabadiliko**: unapaswa kuongeza tabia mpya kwa kuongeza kod mpya, si kwa kuhariri kod ulichojaribu.

## Sauti ambayo OCP inakamatia

```python
# CLOSED to extension: every new shape edits this method (risky, retests everything)
def area(shape):
    if shape.kind == "circle":   return 3.14159 * shape.r ** 2
    elif shape.kind == "square": return shape.s ** 2
    elif shape.kind == "rect":   return shape.w * shape.h
    # add a triangle → modify this function again...
```

Kila aina mpya italazimisha mabadiliko ya safu inayokua ya `if/elif` — nyinzani na sumakanda ya bugs.

## OCP kupitia polimorfizmu

```python
from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self): ...

class Circle(Shape):
    def __init__(self, r): self.r = r
    def area(self): return 3.14159 * self.r ** 2

class Triangle(Shape):                 # NEW behavior = NEW class
    def __init__(self, b, h): self.b, self.h = b, h
    def area(self): return 0.5 * self.b * self.h

def total_area(shapes):                # never changes again
    return sum(s.area() for s in shapes)
```

Kuongeza `Triangle` kunakubali **mabadiliko sifuri** kwa `total_area` — upanuzi bila mabadiliko.

## Mitambo inayowezesha OCP

```text
→ polymorphism / inheritance     → strategy pattern (inject behavior)
→ plugins / interfaces           → higher-order functions / callbacks
```

## Ajali

OCP iliyofanywa kwa dhana inakuwa over-engineering — abstraksioni zilizojengwa kwa tofauti ambayo hazikuja kamwe. Itumia pale ambapo mabadiliko yanawezekana *kabisa* ("sheria ya tatu": kweza baada ya tofauti kuonekana halisi).

## Kwa nini ni muhimu

Kuhariri kod ulichojaribu vizuri kuongeza sifa kunajeopeza regressions katika kila kitu ambacho kod hicho tayari kinasaidiana; OCP hutoa vizuizi kwa tabia mpya kwa vitengo vipya, vilivyotengana.

Ni kanuni iliyong'oana rameworksi zinazoweza kupanuliwa na mifumo ya plugin — na inategemea LSP, kwa sababu aina ndogo zinazobadilishana ndizo zinayofanya kizazi "kilichofungwa" kilichotulivu kusalia hakidhambuliwa.