Struct repr::Row

pub struct Row { /* fields omitted */ }

A packed representation for Datums.

Datum is easy to work with but very space inefficent. A Datum::Int32(42) is laid out in memory like this:

tag: 3 padding: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 data: 0 0 0 42 padding: 0 0 0 0 0 0 0 0 0 0 0 0

For a total of 32 bytes! The second set of padding is needed in case we were to write a Datum::Decimal into this location. The first set of padding is needed to align that hypothetical decimal to a 16 bytes boundary.

A Row stores zero or more Datums without any padding. We avoid the need for the first set of padding by only providing access to the Datums via calls to ptr::read_unaligned, which on modern x86 is barely penalized. We avoid the need for the second set of padding by not providing mutable access to the Datum. Instead, Row is append-only.

A Row can be built from a collection of Datums using Row::pack, but it often more efficient to use and re-use a RowPacker which can avoid unneccesary allocations. The Row::pack_slice method pre-determines the necessary allocation, and is also appropriate.

let row = Row::pack_slice(&[Datum::Int32(0), Datum::Int32(1), Datum::Int32(2)]);
assert_eq!(row.unpack(), vec![Datum::Int32(0), Datum::Int32(1), Datum::Int32(2)])

Rows can be unpacked by iterating over them:

let row = Row::pack_slice(&[Datum::Int32(0), Datum::Int32(1), Datum::Int32(2)]);
assert_eq!(row.iter().nth(1).unwrap(), Datum::Int32(1));

If you want random access to the Datums in a Row, use Row::unpack to create a Vec<Datum>

let row = Row::pack_slice(&[Datum::Int32(0), Datum::Int32(1), Datum::Int32(2)]);
let datums = row.unpack();
assert_eq!(datums[1], Datum::Int32(1));

Performance

Rows are dynamically sized, but up to a fixed size their data is stored in-line. It is best to re-use a RowPacker across multiple Row creation calls, as this avoids the allocations involved in RowPacker::new().

Implementations

impl Row

pub fn pack<'a, I, D>(iter: I) -> Row where
    I: IntoIterator<Item = D>,
    D: Borrow<Datum<'a>>, 

Take some Datums and pack them into a Row.

pub fn try_pack<'a, I, D, E>(iter: I) -> Result<Row, E> where
    I: IntoIterator<Item = Result<D, E>>,
    D: Borrow<Datum<'a>>, 

Like Row::pack, but the provided iterator is allowed to produce an error, in which case the packing operation is aborted and the error returned.

pub unsafe fn new(data: Vec<u8>) -> Self

Creates a new row from supplied bytes.

Safety

This method relies on data being an appropriate row encoding, and can result in unsafety if this is not the case.

pub fn pack_slice<'a>(slice: &[Datum<'a>]) -> Row

Pack a slice of Datums into a Row.

This method has the advantage over pack that it can determine the required allocation before packing the elements, ensuring only one allocation and no redundant copies required.

pub fn unpack(&self) -> Vec<Datum<'_>>

Unpack self into a Vec<Datum> for efficient random access.

pub fn unpack_first(&self) -> Datum<'_>

Return the first Datum in self

Panics if the Row is empty.

pub fn iter(&self) -> DatumListIter<'_>

pub fn data(&self) -> &[u8]

For debugging only

Trait Implementations

impl Clone for Row

fn clone(&self) -> Row

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Row

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

Debug representation using the internal datums

impl Default for Row

fn default() -> Row

Returns the "default value" for a type.

impl<'de> Deserialize<'de> for Row

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error> where
    __D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl Display for Row

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

Display representation using the internal datums

impl Eq for Row

impl Hash for Row

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

Feeds this value into the given Hasher.

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

Feeds a slice of this type into the given Hasher.

impl<'a> IntoIterator for &'a Row

type Item = Datum<'a>

The type of the elements being iterated over.

type IntoIter = DatumListIter<'a>

Which kind of iterator are we turning this into?

fn into_iter(self) -> DatumListIter<'a>

Creates an iterator from a value.

impl Ord for Row

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

#[must_use]pub fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]pub fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]pub fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval.

impl PartialEq<Row> for Row

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

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

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

This method tests for !=.

impl PartialOrd<Row> for Row

These implementations order first by length, and then by slice contents. This allows many comparisons to complete without dereferencing memory.

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

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

#[must_use]pub fn lt(&self, other: &Rhs) -> bool

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

#[must_use]pub fn le(&self, other: &Rhs) -> bool

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

#[must_use]pub fn gt(&self, other: &Rhs) -> bool

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

#[must_use]pub 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 Serialize for Row

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

Serialize this value into the given Serde serializer.

impl StructuralEq for Row

impl StructuralPartialEq for Row