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// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
use zerovec::ule::VarULE;
#[cfg(feature = "alloc")]
use zerovec::{maps::ZeroMapKV, ZeroMap2d};
/// A trait that associates a [`VarULE`] type with a data struct.
///
/// Some data structs can be represented compactly as a single [`VarULE`],
/// such as `str` or a packed pattern. This trait allows for data providers
/// to use optimizations for such types.
///
/// ❗ Not all data structs benefit from this optimization. It works best when the
/// data struct is multiplied across a large number of data marker attributes.
///
/// Both [`MaybeAsVarULE`] and [`MaybeEncodeAsVarULE`] should be implemented
/// on all data structs. The [`data_struct!`](crate::data_struct) macro provides an impl.
pub trait MaybeAsVarULE {
/// The [`VarULE`] type for this data struct, or `[()]`
/// if it cannot be represented as [`VarULE`].
type EncodedStruct: ?Sized + VarULE;
}
/// Export-only trait associated with [`MaybeAsVarULE`]. See that trait
/// for additional details.
///
/// ✨ *Enabled with the `export` Cargo feature.*
#[cfg(feature = "export")]
pub trait MaybeEncodeAsVarULE: MaybeAsVarULE {
/// Returns the [`MaybeAsVarULE::EncodedStruct`] that represents this data struct,
/// or `None` if the data struct does not support this representation.
fn maybe_encode_as_varule(&self) -> Option<&Self::EncodedStruct>;
}
/// Implements required traits on data structs, such as [`MaybeEncodeAsVarULE`].
#[macro_export] // canonical location is crate root
macro_rules! data_struct {
(<$generic:ident: $bound:tt> $ty:path $(, $(#[$attr:meta])*)?) => {
impl<$generic: $bound> $crate::ule::MaybeAsVarULE for $ty {
type EncodedStruct = [()];
}
$($(#[$attr])*)?
impl<$generic: $bound> $crate::ule::MaybeEncodeAsVarULE for $ty {
fn maybe_encode_as_varule(&self) -> Option<&Self::EncodedStruct> {
None
}
}
};
($ty:path $(, $(#[$attr:meta])*)?) => {
impl $crate::ule::MaybeAsVarULE for $ty {
type EncodedStruct = [()];
}
$($(#[$attr])*)?
impl $crate::ule::MaybeEncodeAsVarULE for $ty {
fn maybe_encode_as_varule(&self) -> Option<&Self::EncodedStruct> {
None
}
}
};
(
$ty:ty,
varule: $varule:ty,
$(#[$attr:meta])*
encode_as_varule: $encode_as_varule:expr
) => {
impl<'data> $crate::ule::MaybeAsVarULE for $ty {
type EncodedStruct = $varule;
}
$(#[$attr])*
impl<'data> $crate::ule::MaybeEncodeAsVarULE for $ty {
fn maybe_encode_as_varule(&self) -> Option<&Self::EncodedStruct> {
fn bind_lifetimes<F>(f: F) -> F where F: for<'data> Fn(&'data $ty) -> &'data $varule { f }
Some(bind_lifetimes($encode_as_varule)(self))
}
}
};
}
//=== Standard impls ===//
#[cfg(feature = "alloc")]
impl<'a, K0, K1, V> MaybeAsVarULE for ZeroMap2d<'a, K0, K1, V>
where
K0: ZeroMapKV<'a>,
K1: ZeroMapKV<'a>,
V: ZeroMapKV<'a>,
K0: ?Sized,
K1: ?Sized,
V: ?Sized,
{
type EncodedStruct = [()];
}
#[cfg(feature = "alloc")]
#[cfg(feature = "export")]
impl<'a, K0, K1, V> MaybeEncodeAsVarULE for ZeroMap2d<'a, K0, K1, V>
where
K0: ZeroMapKV<'a>,
K1: ZeroMapKV<'a>,
V: ZeroMapKV<'a>,
K0: ?Sized,
K1: ?Sized,
V: ?Sized,
{
fn maybe_encode_as_varule(&self) -> Option<&Self::EncodedStruct> {
None
}
}
impl<T, const N: usize> MaybeAsVarULE for [T; N] {
type EncodedStruct = [()];
}
#[cfg(feature = "export")]
impl<T, const N: usize> MaybeEncodeAsVarULE for [T; N] {
fn maybe_encode_as_varule(&self) -> Option<&Self::EncodedStruct> {
None
}
}