Struct blockbuffers::position::TablePosition

pub struct TablePosition(pub usize);

TablePosition wrappers a position which points to a table in the buffer.

They start with an soffset_t to a vtable. This is a signed version of uoffset_t, since vtables may be stored anywhere relative to the object. This offset is substracted (not added) from the object start to arrive at the vtable start. This offset is followed by all the fields as aligned scalars (or offsets). Unlike structs, not all fields need to be present. There is no set order and layout.

To be able to access fields regardless of these uncertainties, we go through a vtable of offsets. Vtables are shared between any objects that happen to have the same vtable values.

Tuple Fields

0: usize

Implementations

impl TablePosition

pub fn vtable(self, buf: &[u8]) -> VTablePosition

Seeks the vtable position.

Examples

use blockbuffers::position::TablePosition;
//         | -4               | vtable      | 4         |
let buf = &[252, 255, 255, 255, 4u8, 0, 4, 0, 4, 0, 0, 0][..];

let pos1 = TablePosition(0);
assert_eq!(4, pos1.vtable(&buf).0);
let pos2 = TablePosition(8);
assert_eq!(4, pos2.vtable(&buf).0);

pub fn field_position(self, buf: &[u8], pos_in_vtable: usize) -> Option<usize>

Seeks the position for a field.

The field index is specified using pos_in_vtable, which is the offset inside vtable bytes. For example, 4 means the first field, 6 is the second.

Examples

use blockbuffers::position::TablePosition;
//       [vtable 10|    40|    20|    0|    4] [table   10]
let buf = &[10u8, 0, 40, 0, 20, 0, 0, 0, 4, 0, 10, 0, 0, 0][..];
let pos = TablePosition(10);

assert_eq!(Some(20 + 10), pos.field_position(&buf, 4));
assert_eq!(None, pos.field_position(&buf, 6));
assert_eq!(Some(4 + 10), pos.field_position(&buf, 8));
assert_eq!(None, pos.field_position(&buf, 10));

Trait Implementations

impl Clone for TablePosition

fn clone(&self) -> TablePosition

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for TablePosition

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

Formats the value using the given formatter.

impl PartialEq<TablePosition> for TablePosition

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

This method tests for self and other values to be equal, and is used by ==.

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

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

impl PartialOrd<TablePosition> for TablePosition

fn partial_cmp(&self, other: &TablePosition) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

This method tests less than (for self and other) and is used by the < operator.

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Copy for TablePosition

impl StructuralPartialEq for TablePosition