Jelasake Prinsip Open/Closed kanthi jero.

Question

Accepted Answer

**Prinsip Open/Closed (OCP)** nyebutake manawa entitas piranti lunak kudu **mbukak kanggo extension nanging nutup kanggo modifikasi**: sampeyan kudu nambah tingkah laku anyar kanthi nambah kode anyar, ora kanthi nyunting kode sing wis ana lan wis diuji.

## Menapa penting

```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...
```

Saben jenis anyar ngejeksa owah-owahan kanthi chain `if/elif` sing berkembang — rawan lan magnet kanggo bug.

## OCP liwat polimorfisme

```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)
```

Nambah `Triangle` merlokake **modifikasi nol** kanggo `total_area` — extension tanpa modifikasi.

## Mekanisme sing aktifake OCP

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

## Jebakan

OCP sing ditindakake spekulatif dadi over-engineering — abstraksi sing dibangun kanggo variasi sing ora tau teka. Terapake ing mangsa owah-owahan *kamungkinan besar* ("aturan telu": abstraksi sawise variasi bener-bener katon).

## Menapa penting

Nyunting kode sing wis diuji kanthi keras kanggo nambah fitur mbebayani regresi ing kabeh sing didukung kode kasebut; OCP ngonfinasi tingkah laku anyar menyang unit anyar lan terisolir.

Iki prinsip ing mburi framework sing bisa dikembangke lan sistem plugin — lan iki gumantung OHP, amarga subtipe sing bisa dipantokke yaiku apa sing nggawe inti "nutup" aman kanggo ditinggal ora disentuh.