X'inhuma l-coupling u l-cohesion?

Question

Accepted Answer

**Coupling** ikejjel kemm modulu wieħed jiddependi fuq ieħor; **cohesion** ikejjel kemm b'qawwa l-partijiet *ġewwa* modulu japparten flimkien. L-għan: **coupling baxx, cohesion għoli**.

## It-taqqas tnejn

```text
HIGH cohesion  → a class does ONE well-defined job, parts relate strongly  ✅
LOW  coupling  → modules interact through small, stable interfaces         ✅
```

## Cohesion baxx (ħażin) versus cohesion għoli (tajjeb)

```python
# LOW cohesion: unrelated responsibilities jammed together
class Utils:
    def parse_csv(self, s): ...
    def send_email(self, to): ...
    def hash_password(self, p): ...   # nothing in common

# HIGH cohesion: each class has a single, focused purpose
class CsvParser:     ...
class Mailer:        ...
class PasswordHasher: ...
```

## Coupling stretti versus coupling ħelwa

```python
# TIGHT: OrderService is welded to a concrete class
class OrderService:
    def __init__(self):
        self.db = MySqlDatabase()        # can't swap or test in isolation

# LOOSE: depends on an abstraction, injected in
class OrderService:
    def __init__(self, db: Database):    # any Database works
        self.db = db
```

Coupling ħelwa jippermettilك tara `MySqlDatabase` b'fake f-memorja għat-tests, mingħajr edita sa `OrderService`.

## Għaliex ikun importanti

Coupling stretti huwa dak li jagħmel bidla "ripple" — imiss klassь wieħed u għaxra oħrajn jinqasmu; coupling ħelwa jwaqqaf il-bidliet lejn is-sors tagħhom.

Cohesion għoli jagħmel il-kodiċi jista' jinstab u jista' jiġi ttestjat: meta klassь tagħmel ħaġa waħda, taf fejn jgħix il-loġika u x'ħaġa test għandha tkopri.

Il-metriċi tnejn hawa fuq pratikament kull prinċipju ta' disinn ieħor.