Struct Span 

pub struct Span {
    pub start: u32,
    pub len: u32,
}

a region of the source: start is a byte offset, len is a byte length.

u32 fields cap a source file at 4 GiB, which is fine for a single-file teaching language and halves the struct size against usize. Copy matters because spans are attached to every token and every AST node and get cloned constantly.

Fields

start: u32

byte offset of the first byte of this region, from the start of the source.

len: u32

length of this region in bytes.

Implementations

impl Span

pub fn new(start: usize, len: usize) -> Self

construct a span from a byte offset and a byte length.

pub fn end(self) -> usize

the byte offset one past the last byte of this region (start + len).

pub fn merge(self, other: Span) -> Span

the smallest span covering both inputs.

uses min on the start and max on the end, so the result is correct regardless of argument order and whether the two spans overlap, touch, or have a gap between them. the parser uses this to span a whole expression from its first token to its last.

pub fn to(self, other: Span) -> Span

alias for Span::merge; reads better at parser call sites (first.to(last)).

pub fn slice(self, src: &str) -> &str

the source text this span covers.

the caller must pass the same source the span was produced from; the span indexes it with its own start and end, both of which the scanner produced on UTF-8 boundaries.

Trait Implementations

impl Clone for Span

fn clone(&self) -> Span

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Span

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Span

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Hash for Span

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Span

fn eq(&self, other: &Span) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for Span

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for Span

impl Eq for Span

impl StructuralPartialEq for Span