Module jlrs::layout::bits_union [−][src]
Expand description
Enforce layout requirements of bits union fields.
If a field of a Julia type is a union of several bits types, this field is stored in an interesting way: the field will have the same alignment as the type in the union with the largest alignment, and the same size as the type with the largest size, after the data a single-byte flag is stored which indicates what the active variant is. Unlike normal struct fields, the size doesn’t have to be a multiple of the alignment. This is unlike structs in Rust, whose size is a multiple of their alignment.
In order represent such a union in Rust, JlrsReflect.jl generates three separate fields: an zero-sized alignment field which enforces the alignment, a container to store the raw bytes, and a flag to indicate the active variant.
This module provides three traits, one for each of the fields. Align ensures the next
field, which contains the data of the bits-union, is aligned correctly. BitsUnionContainer
and Flag are essentially marker traits that are used by jlrs-derive to implement
ValidLayout correctly.
Traits
Trait implemented by the aligning structs, which ensure bits unions are properly aligned.
Used in combination with BitsUnionContainer and Flag to ensure bits unions are inserted
correctly.
Trait implemented by structs that can contain the data of a bits union. Used in combination
with Align and Flag to ensure bits unions are inserted correctly.
Trait implemented by structs that can contain the flag of a bits union. Used in combination
with Align and BitsUnionContainer to ensure bits unions are inserted correctly.