Two fields that should agree, and don't.
The problem
A flag you have to keep in sync.
int _health = 100;bool _isDead; public void TakeDamage( int amount ){ _health -= amount; if ( _health <= 0 ) _isDead = true;} public void Poison() => _health -= 5;
Poison lowers health but never sets the flag. Every new way to lose health is a new chance to forget.
The fix
Work it out when you're asked.
If a value can be calculated from other values, calculate it. Then it can never be out of date.
IsDead=>_health <= 0
The fix in code
A property with an arrow.
int _health = 100; public bool IsDead => _health <= 0; public void TakeDamage( int amount ) => _health -= amount;public void Poison() => _health -= 5;
No flag to set. However health drops, IsDead is right the next time anyone reads it.
Watch out
It runs every time you read it.
Keep computed properties cheap. Whatever is in there runs on every single read.
- A comparison
- free, keep it
- A search of the scene
- store it instead
- Read in a loop
- the cost multiplies
The rule
If you can calculate it, don't store it.
- Derived value
- => expression
- No flag
- nothing to forget
- Expensive work
- cache it instead