switch-exhaustiveness-check
)Union type may have a lot of parts. It's easy to forget to consider all cases in switch. This rule reminds which parts are missing. If domain of the problem requires to have only a partial switch, developer may explicitly add a default clause.
Examples of incorrect code for this rule:
type Day = | 'Monday' | 'Tuesday' | 'Wednesday' | 'Thursday' | 'Friday' | 'Saturday' | 'Sunday'; const day = 'Monday' as Day; let result = 0; switch (day) { case 'Monday': { result = 1; break; } }
Examples of correct code for this rule:
type Day = | 'Monday' | 'Tuesday' | 'Wednesday' | 'Thursday' | 'Friday' | 'Saturday' | 'Sunday'; const day = 'Monday' as Day; let result = 0; switch (day) { case 'Monday': { result = 1; break; } case 'Tuesday': { result = 2; break; } case 'Wednesday': { result = 3; break; } case 'Thursday': { result = 4; break; } case 'Friday': { result = 5; break; } case 'Saturday': { result = 6; break; } case 'Sunday': { result = 7; break; } }
or
type Day = | 'Monday' | 'Tuesday' | 'Wednesday' | 'Thursday' | 'Friday' | 'Saturday' | 'Sunday'; const day = 'Monday' as Day; let result = 0; switch (day) { case 'Monday': { result = 1; break; } default: { result = 42; } }
If program doesn‘t have union types with many parts. Downside of this rule is the need for type information, so it’s slower than regular rules.