Struct PackedPatterns

pub struct PackedPatterns<'data> {
    pub header: u32,
    pub elements: VarZeroVec<'data, PluralElementsPackedULE<ZeroSlice<PatternItem>>>,
}

📏 This item has a stack size of 32 bytes on the stable toolchain at release date.

Variants

This supports a set of “standard” patterns plus up to two “variants”. The variants are currently used by year formatting:

• Standard: Year, which could be partial precision (2-digit Gregorian)
• Variant 0: Full Year, which is always full precision
• Variant 1: Year With Era

And by time formatting:

• Standard: Hour only
• Variant 0: Hour and minute
• Variant 1: Hour, minute, and second

Variants should be used when the pattern could depend on the value being formatted. For example, with YearStyle::Auto, any of these three patterns could be selected based on the year value.

Representation

Currently, there are at most 9 patterns that need to be stored together, named according to this table:

	Standard	Variant 0	Variant 1
Long	La	Lb	Lc
Medium	Ma	Mb	Mc
Short	Sa	Sb	Sc

The header byte encodes which pattern in the patterns array corresponds to a particular cell in the table. It contains the following information:

• Bits 0-1: “LMS” value of the standard column
• Bit 2: “Q” value: 1 for directly-indexed variants; 0 for per-cell offsets
• Bits 3-20: Packed offset into patterns table for each variant cell
• Bits 21-31: unused/reserved

The LMS value determines which pattern index is used for the first column:

LMS Value	Long Index	Medium Index	Short Index
0 (L=M=S)	0	0	0
1 (L, M=S)	0	1	1
2 (L=M, S)	0	0	1
3 (L, M, S)	0	1	2

If bit 2 is 1 (Q=1), it means there is one pattern per table cell, with the index offset by the short index S from the table above. However, this requires storing multiple, possibly duplicate, patterns in the packed structure. The more common case is Q=0 and then to store per-cell offsets in chunks of 3 bits per cell:

• Chunk = 0: Inherit according to the table below
• Chunk = 1-7: Use pattern index Chunk - 1

This is summarized below:

Cell in Table	Q=1 Pattern Index	Q=0 Header Bits	Inheritance
Lb	S + 1	3-5	La
Mb	S + 2	6-8	Ma
Sb	S + 3	9-11	Sa
Lc	S + 4	12-14	La
Mc	S + 5	15-17	Ma
Sc	S + 6	18-20	Sa

As a result, if there are no variants, bits 2 and higher will be all zero, making the header int suitable for varint packing, such as that used by postcard and other size-optimized serialization formats.

Fields

header: u32

An encoding of which standard/variant cell corresponds to which entry in the patterns table. See class docs.

elements: VarZeroVec<'data, PluralElementsPackedULE<ZeroSlice<PatternItem>>>

The list of patterns. Length should be between 1 and 9, depending on the header.

Implementations

impl PackedPatterns<'_>

pub fn to_builder(&self) -> PackedPatternsBuilder<'_>

Converts this packed data to a builder that can be mutated.

Trait Implementations

impl<'data> Clone for PackedPatterns<'data>

fn clone(&self) -> PackedPatterns<'data>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<'data> Debug for PackedPatterns<'data>

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

Formats the value using the given formatter.

impl<'de, 'data> Deserialize<'de> for PackedPatterns<'data>

where 'de: 'data,

fn deserialize<D>( deserializer: D, ) -> Result<PackedPatterns<'data>, <D as Deserializer<'de>>::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl MaybeAsVarULE for PackedPatterns<'_>

type EncodedStruct = [()]

The VarULE type for this data struct, or [()] if it cannot be represented as VarULE.

impl<'data> PartialEq for PackedPatterns<'data>

fn eq(&self, other: &PackedPatterns<'data>) -> 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<'a> Yokeable<'a> for PackedPatterns<'static>

type Output = PackedPatterns<'a>

This type MUST be Self with the 'static replaced with 'a, i.e. Self<'a>

fn transform(&'a self) -> &'a <PackedPatterns<'static> as Yokeable<'a>>::Output

This method must cast self between &'a Self<'static> and &'a Self<'a>.

fn transform_owned(self) -> <PackedPatterns<'static> as Yokeable<'a>>::Output

This method must cast self between Self<'static> and Self<'a>.

unsafe fn make( this: <PackedPatterns<'static> as Yokeable<'a>>::Output, ) -> PackedPatterns<'static>

This method can be used to cast away Self<'a>’s lifetime.

fn transform_mut<F>(&'a mut self, f: F)

where F: 'static + for<'b> FnOnce(&'b mut <PackedPatterns<'static> as Yokeable<'a>>::Output),

This method must cast self between &'a mut Self<'static> and &'a mut Self<'a>, and pass it to f.

impl<'zf, 'zf_inner> ZeroFrom<'zf, PackedPatterns<'zf_inner>> for PackedPatterns<'zf>

fn zero_from(this: &'zf PackedPatterns<'zf_inner>) -> PackedPatterns<'zf>

Clone the other C into a struct that may retain references into C.

impl<'data> Eq for PackedPatterns<'data>

impl<'data> StructuralPartialEq for PackedPatterns<'data>