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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
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
use crate::Error;
use writeable::{TryWriteable, Writeable};
#[cfg(feature = "alloc")]
use alloc::{borrow::Cow, boxed::Box};
/// A borrowed item in a [`Pattern`]. Items are either string literals or placeholders.
///
/// [`Pattern`]: crate::Pattern
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
#[allow(clippy::exhaustive_enums)] // Part of core data model
pub enum PatternItem<'a, T> {
/// A placeholder of the type specified on this [`PatternItem`].
Placeholder(T),
/// A string literal. This can occur in one of three places:
///
/// 1. Between the start of the string and the first placeholder (prefix)
/// 2. Between two placeholders (infix)
/// 3. Between the final placeholder and the end of the string (suffix)
Literal(&'a str),
}
/// A borrowed-or-owned item in a [`Pattern`]. Items are either string literals or placeholders.
///
/// ✨ *Enabled with the `alloc` Cargo feature.*
///
/// [`Pattern`]: crate::Pattern
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
#[allow(clippy::exhaustive_enums)] // Part of core data model
#[cfg(feature = "alloc")]
#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
pub enum PatternItemCow<'a, T> {
/// A placeholder of the type specified on this [`PatternItemCow`].
Placeholder(T),
/// A string literal. This can occur in one of three places:
///
/// 1. Between the start of the string and the first placeholder (prefix)
/// 2. Between two placeholders (infix)
/// 3. Between the final placeholder and the end of the string (suffix)
#[cfg_attr(feature = "serde", serde(borrow))]
Literal(Cow<'a, str>),
}
#[cfg(feature = "alloc")]
impl<'a, T, U> From<PatternItem<'a, U>> for PatternItemCow<'a, T>
where
T: From<U>,
{
fn from(value: PatternItem<'a, U>) -> Self {
match value {
PatternItem::Placeholder(t) => Self::Placeholder(t.into()),
PatternItem::Literal(s) => Self::Literal(Cow::Borrowed(s)),
}
}
}
/// Types that implement backing data models for [`Pattern`] implement this trait.
///
/// The trait has no public methods and is not implementable outside of this crate.
///
/// [`Pattern`]: crate::Pattern
// Debug so that `#[derive(Debug)]` on types generic in `PatternBackend` works
pub trait PatternBackend: crate::private::Sealed + 'static + core::fmt::Debug {
/// The type to be used as the placeholder key in code.
type PlaceholderKey<'a>;
/// Cowable version of the type to be used as the placeholder key in code.
// Note: it is not good practice to feature-gate trait methods, but this trait is sealed
#[cfg(feature = "alloc")]
type PlaceholderKeyCow<'a>;
/// The type of error that the [`TryWriteable`] for this backend can return.
type Error<'a>;
/// The unsized type of the store required for this backend, usually `str` or `[u8]`.
#[doc(hidden)] // TODO(#4467): Should be internal
type Store: ?Sized + PartialEq + core::fmt::Debug;
/// The iterator type returned by [`Self::try_from_items`].
#[doc(hidden)] // TODO(#4467): Should be internal
type Iter<'a>: Iterator<Item = PatternItem<'a, Self::PlaceholderKey<'a>>>;
/// Checks a store for validity, returning an error if invalid.
#[doc(hidden)] // TODO(#4467): Should be internal
fn validate_store(store: &Self::Store) -> Result<(), Error>;
/// Constructs a store from pattern items.
#[doc(hidden)]
// TODO(#4467): Should be internal
// Note: it is not good practice to feature-gate trait methods, but this trait is sealed
#[cfg(feature = "alloc")]
fn try_from_items<
'cow,
'ph,
I: Iterator<Item = Result<PatternItemCow<'cow, Self::PlaceholderKeyCow<'ph>>, Error>>,
>(
items: I,
) -> Result<Box<Self::Store>, Error>;
/// Iterates over the pattern items in a store.
#[doc(hidden)] // TODO(#4467): Should be internal
fn iter_items(store: &Self::Store) -> Self::Iter<'_>;
/// The store for the empty pattern, used to implement `Default`
#[doc(hidden)] // TODO(#4467): Should be internal
fn empty() -> &'static Self::Store;
}
/// Trait implemented on collections that can produce [`TryWriteable`]s for interpolation.
///
/// This trait can add [`Part`]s for individual literals or placeholders. The implementations
/// of this trait on standard types do not add any [`Part`]s.
///
/// # Examples
///
/// A custom implementation that adds parts:
///
/// ```
/// use core::str::FromStr;
/// use icu_pattern::Pattern;
/// use icu_pattern::DoublePlaceholder;
/// use icu_pattern::DoublePlaceholderKey;
/// use icu_pattern::PlaceholderValueProvider;
/// use writeable::adapters::WithPart;
/// use writeable::adapters::WriteableAsTryWriteableInfallible;
/// use writeable::assert_writeable_parts_eq;
/// use writeable::Part;
/// use writeable::Writeable;
///
/// let pattern = Pattern::<DoublePlaceholder>::try_from_str(
/// "Hello, {0} and {1}!",
/// Default::default(),
/// )
/// .unwrap();
///
/// struct ValuesWithParts<'a>(&'a str, &'a str);
///
/// const PART_PLACEHOLDER_0: Part = Part {
/// category: "custom",
/// value: "placeholder0",
/// };
/// const PART_PLACEHOLDER_1: Part = Part {
/// category: "custom",
/// value: "placeholder1",
/// };
/// const PART_LITERAL: Part = Part {
/// category: "custom",
/// value: "literal",
/// };
///
/// impl PlaceholderValueProvider<DoublePlaceholderKey> for ValuesWithParts<'_> {
/// type Error = core::convert::Infallible;
///
/// type W<'a> = WriteableAsTryWriteableInfallible<WithPart<&'a str>>
/// where
/// Self: 'a;
///
/// type L<'a, 'l> = WithPart<&'l str>
/// where
/// Self: 'a;
///
/// #[inline]
/// fn value_for(&self, key: DoublePlaceholderKey) -> Self::W<'_> {
/// let writeable = match key {
/// DoublePlaceholderKey::Place0 => WithPart {
/// writeable: self.0,
/// part: PART_PLACEHOLDER_0,
/// },
/// DoublePlaceholderKey::Place1 => WithPart {
/// writeable: self.1,
/// part: PART_PLACEHOLDER_1,
/// },
/// };
/// WriteableAsTryWriteableInfallible(writeable)
/// }
///
/// #[inline]
/// fn map_literal<'a, 'l>(&'a self, literal: &'l str) -> Self::L<'a, 'l> {
/// WithPart {
/// writeable: literal,
/// part: PART_LITERAL,
/// }
/// }
/// }
///
/// assert_writeable_parts_eq!(
/// pattern.interpolate(ValuesWithParts("Alice", "Bob")),
/// "Hello, Alice and Bob!",
/// [
/// (0, 7, PART_LITERAL),
/// (7, 12, PART_PLACEHOLDER_0),
/// (12, 17, PART_LITERAL),
/// (17, 20, PART_PLACEHOLDER_1),
/// (20, 21, PART_LITERAL),
/// ]
/// );
/// ```
///
/// [`Part`]: writeable::Part
pub trait PlaceholderValueProvider<K> {
type Error;
/// The type of [`TryWriteable`] returned by [`Self::value_for`].
///
/// To return a [`Writeable`], wrap it with [`WriteableAsTryWriteableInfallible`].
///
/// [`WriteableAsTryWriteableInfallible`]: writeable::adapters::WriteableAsTryWriteableInfallible
type W<'a>: TryWriteable<Error = Self::Error>
where
Self: 'a;
/// The type of [`Writeable`] returned by [`Self::map_literal`].
///
/// If you are not adding parts, this can be `&'l str`.
type L<'a, 'l>: Writeable
where
Self: 'a;
/// Returns the [`TryWriteable`] to substitute for the given placeholder.
///
/// See [`PatternItem::Placeholder`]
fn value_for(&self, key: K) -> Self::W<'_>;
/// Maps a literal string to a [`Writeable`] that could contain parts.
///
/// See [`PatternItem::Literal`]
fn map_literal<'a, 'l>(&'a self, literal: &'l str) -> Self::L<'a, 'l>;
}
impl<'b, K, T> PlaceholderValueProvider<K> for &'b T
where
T: PlaceholderValueProvider<K> + ?Sized,
{
type Error = T::Error;
type W<'a>
= T::W<'a>
where
Self: 'a;
type L<'a, 'l>
= T::L<'a, 'l>
where
Self: 'a;
fn value_for(&self, key: K) -> Self::W<'_> {
(*self).value_for(key)
}
fn map_literal<'a, 'l>(&'a self, literal: &'l str) -> Self::L<'a, 'l> {
(*self).map_literal(literal)
}
}