Struct Label

pub struct Label(pub Rc<RealLabel>);

A Label represents a value not yet known that is stored in a Section.

As long as all the labels a section refers to are defined by the time its contents are retrieved as bytes, undefined labels can be used freely in that section’s construction. A label can be in one of three states:

• undefined,
• defined as the sum of some other label and a constant, or
• a constant.

A label’s value never changes, but it can accumulate constraints. Adding labels and integers is permitted, and yields a label. Subtracting a constant from a label is permitted, and also yields a label. Subtracting two labels that have some relationship to each other is permitted, and yields a constant.

A common usage of Label is to use Section::mark to make a Label contain an offset into the Section without having to hard-code it. The Section methods for inserting fixed-width integer values (such as Section::L32) all accept &Label for the purpose of writing a value that is not yet available.

Examples

Labels can be set to point to other Labels, potentially with an offset.

use test_assembler::*;

let l1 = Label::new();
// l2 is l1's value (which is currently undefined) + 10
let l2 = &l1 + 10;
// Now give l1 a value.
l1.set_const(1);
// l2's value is derived from l1.
assert_eq!(l2.value().unwrap(), 11);

Tuple Fields

0: Rc<RealLabel>

Trait Implementations

impl<'a> Add<i64> for &'a Label

Add a constant to a Label, producing a new Label.

The new Label references the existing Label.

type Output = Label

The resulting type after applying the + operator.

fn add(self, rhs: i64) -> Label

Performs the + operation.

impl Clone for Label

fn clone(&self) -> Label

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Label

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Deref for Label

type Target = RealLabel

The resulting type after dereferencing.

fn deref(&self) -> &RealLabel

Dereferences the value.

impl LabelMaker for Label

fn new() -> Label

Create an undefined label.

fn from_const(val: u64) -> Label

Create a label with a constant value val.

fn from_label(other: &Label) -> Label

Create a label whose value is equal to other.

fn from_label_offset(other: &Label, offset: i64) -> Label

Create a label whose value is equal to other plus offset.

impl<'a> Sub<i64> for &'a Label

Subtract a constant from a Label, producing a new Label.

The new Label references the existing Label.

type Output = Label

The resulting type after applying the - operator.

fn sub(self, rhs: i64) -> Label

Performs the - operation.

impl<'a> Sub for &'a Label

Subtract a Label from another Label, returning an i64.

If the labels are unrelated this will panic.

type Output = i64

The resulting type after applying the - operator.

fn sub(self, rhs: &'a Label) -> i64

Performs the - operation.

impl<'a, T: Num> ToLabelOrNum<'a, T> for &'a Label

fn to_labelornum(self) -> LabelOrNum<T>

impl<'a, T: Num> ToLabelOrNum<'a, T> for Label

fn to_labelornum(self) -> LabelOrNum<T>