Types
Types
This chapter describes the type system of Gruel.
Every value in Gruel has a type that determines its representation in memory and the operations that can be performed on it.
Zero-Sized Types
A zero-sized type (ZST) is a type with a size of zero bytes. Zero-sized types can be instantiated and passed by value, but they occupy no storage.
The following types are zero-sized:
- The unit type
() - The never type
! - Empty structs (structs with no fields)
- Zero-length arrays
[T; 0]for any typeT
Zero-sized types have an alignment of 1 byte.
Layout Guarantees
Every type in Gruel has a defined size (in bytes) and alignment, observable via the @size_of(T) and @align_of(T) intrinsics. The size and alignment of any given type are stable: two compilations of the same program with the same compiler version, target, and feature set yield the same numbers.
The specific in-memory representation of a value — including the presence, position, and width of any internal discriminant — is an implementation choice except where this specification explicitly guarantees otherwise. Implementations may use alternative encodings such as niche-filling for enums whose payload type forbids certain bit patterns. The @size_of result for a type may shrink under such optimizations.
The only portable observables of a value are: pattern matching, equality (== / !=), field access on structs, payload-binding pattern matches on enums, indexing on arrays, and the @size_of / @align_of intrinsics. Programs that interpret the raw bytes of a value depend on the implementation-defined representation and are not guaranteed to be portable across compiler versions.