zig/doc/codegen.md

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2016-08-23 15:05:26 -07:00
# Code Generation
## Data Representation
Every type has a "handle". If a type is a simple primitive type such as i32 or
f64, the handle is "by value", meaning that we pass around the value itself when
we refer to a value of that type.
If a type is a container, error union, maybe type, slice, or array, then its
handle is a pointer, and everywhere we refer to a value of this type we refer to
a pointer.
Parameters and return values are always passed as handles.
Error union types are represented as:
struct {
error: u32,
payload: T,
}
Maybe types are represented as:
struct {
payload: T,
is_non_null: u1,
}
## Data Optimizations
Maybe pointer types are special: the 0x0 pointer value is used to represent a
null pointer. Thus, instead of the struct above, maybe pointer types are
represented as a `usize` in codegen and the handle is by value.