Type system overview

The Tolk type system is designed with the specifics of TON in mind.

Since on-chain data and communication rely entirely on cells, the system focuses on binary serialization and clear data relationships.

Programs run on a stack-based virtual machine (TVM), which imposes specific rules on how values are represented at runtime.

This section describes all the types in Tolk language:

• numbers — int, int32, uint64, coins, etc.
• boolean — true/false and logical operators
• address — internal, external, and none addresses
• cells — and also slices, builders, and raw bits
• strings — not a native type, emulated using slices
• structures — group several fields into one entity
• type aliases — similar to TypeScript and Rust
• generics — any struct can be generic <T>
• enums — a distinct type containing integer variants
• nullable types — with null safety and smart casts
• union types — a variable holds one of possible values
• tensors — multiple values placed sequentially on the stack
• tuples — multiple values stored in a single TVM tuple
• maps — key-value dictionaries
• callables — first-class functions
• void and never — both mean “absence of a value”

An article “Type checks and casts” describes casting types with unsafe as operator.

For a summary of how types are represented on a TVM stack, follow Overall: TVM stack representation.

For a summary of how types are serialized and their relation to TL/B, follow Overall: serialization.