Type system overview

Tolk has the following types:

• numbers — int, int32, uint64, coins, and others.
• boolean — true and false.
• address — internal, external, and none.
• cells — containers with up to 1023 bits of data and up to 4 references to other cells, plus the cell manipulation primitives of TVM: builders and slices.
• structures — multiple fields grouped into one entity.
• generics — any struct can be generic <T>.
• enums — distinct types containing integer variants.
• nullable types — null safety and safe casts.
• union types — variables holding one of several possible values.
• strings — string values stored as snake-encoded cells.
• tensors — multiple values placed sequentially on the stack.
• arrays — dynamically sized containers backed by TVM tuples.
• maps — key-value dictionaries.
• callables — first-class functions.
• unknown — any value that is a single-slot TVM primitive.
• void and never — both represent the absence of a value.

To make an interchangeable alias for an existing type, including structural types, there are type aliases.

Smart contracts run on a stack-based virtual machine, TVM, which imposes specific rules on how values are represented at runtime. For example, strings are stored as snake-encoded cells, because TVM has no native string support.

All on-chain data and communication rely entirely on cells, so the type system focuses on binary serialization and clear data relationships:

• Type checks and casts covers casting with the unsafe as operator.
• TVM stack representation summarizes how types map to the TVM stack.
• Serialization describes how types serialize and relate to TL-B.