logos.mem.writ.tag_system
Module mem · package logos-mem
Traits
traitTagSystem
trait TagSystemEncapsulates how a type tag (type_code) is read from a raw memory object.
Each impl receives a pointer to the first byte of the object and locates the
tag according to its format.
Implemented by: WritTypeTagSystem DataTypeTagSystem WritTagSystem TomTagSystem
Types
structDataTypeTagSystem
struct DataTypeTagSystemReads the vlen datatag of user Writ zone datatypes (#[type_code=N]).
Same 1-8 byte pre-object format and decoder as WritTypeTagSystem.
Implements: TagSystem
Methods
fn read_tag(self: &DataTypeTagSystem, obj: *const u8) -> u64structTomTagSystem
struct TomTagSystemReads the TOM (TinyObjectMap) tag: the little-endian u64 at byte offset 0 of the
object header. Code 0 is the unset/invalid sentinel; callers reject it as needed.
Implements: TagSystem
Methods
fn read_tag(self: &TomTagSystem, obj: *const u8) -> u64Reads the tag byte-by-byte (no alignment requirement on obj);
returns 0 if the pointer arithmetic would overflow.
structWritTagSystem
struct WritTagSystemReads the vlen tag of Writ arena objects reached via self-relative RelAny/RelPtr.
Same format as WritTypeTagSystem, but a deliberately separate dispatch namespace:
one type_code may carry a base-relative impl there and a self-relative impl here.
Implements: TagSystem
Methods
fn read_tag(self: &WritTagSystem, obj: *const u8) -> u64structWritTypeTagSystem
struct WritTypeTagSystemReads the vlen TypeTag of Writ core zone datatypes: variable-length bytes
immediately before the object. obj[-1] in 1..=222 is the type_code itself;
223+ heads a multi-byte little-endian code. Tag value = type_code (u64).
Implements: TagSystem
Methods
fn read_tag(self: &WritTypeTagSystem, obj: *const u8) -> u64Functions
fnw_tag_size
fn w_tag_size(code: u64) -> i64Returns the byte length of the vlen datatag for code: 0 for the unset code 0,
1 for codes 1..=222, else 1 header byte + N little-endian code bytes.
fnwrite_tag
fn write_tag(obj: *mut u8, type_code: u64) -> voidWrites the vlen datatag for type_code immediately before obj (alias of
w_write_tag; tests and user datatypes write tags by this historical name).
Safety: the tag bytes below obj must be reserved and writable.