nullsafety

Null safety is a feature in programming languages that prevents null reference errors by distinguishing between nullable and non-nullable types. It aims to avoid runtime crashes when a value expected to be present is absent. The concept addresses the so-called billion-dollar mistake of null references. In a null-safe language, variables are typically non-null by default, and nulls are allowed only when explicitly declared.

How it works: the type system enforces checks at compile time, or before runtime, ensuring that operations on values consider their nullability. Many implementations provide syntax for declaring nullable types (for example, in Dart with String? or in Kotlin with String?), and operators for safe access and default values, such as optional chaining and null-coalescing.

Adoption and examples: Dart introduced sound null safety with stable support in 2020. Kotlin has had null safety since its early versions. TypeScript provides strictNullChecks to enforce non-nullability of values by default. Other languages, including Swift and C#, incorporate similar mechanisms. The goal is to reduce runtime null dereferences, while still allowing nulls when truly necessary.

Limitations: migrating existing codebases can be labor-intensive; overuse of nullable types can hamper readability; some runtime edge cases may persist in interoperable or legacy code. Overall, null safety strengthens type guarantees and improves program reliability.