treaty -


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use crate::{
    any::{BorrowedStatic, OwnedStatic, TempBorrowedStatic},
    effect::{Effect, EffectExt as _, Effective, EffectiveExt as _, ErasedEffective},
    never::Never,
    protocol::{
        visitor::{visit_value, EffectiveVisitExt as _, VisitResult},
        DynVisitor,
    },
};

/// A very basic walker that uses the [`Value`][crate::protocol::visitor::value::Value] protocol.
///
/// Primitive types use this walker as their main walker.
/// This walker doesn't consider it an error if the visitor doesn't have the protocol.
#[derive(Debug)]
pub struct ValueWalker<T>(T);

impl<T> ValueWalker<T> {
    /// Create walker from a value.
    #[inline(always)]
    pub fn new(value: T) -> Self {
        Self(value)
    }
}

impl<T> From<T> for ValueWalker<T> {
    #[inline(always)]
    fn from(value: T) -> Self {
        Self::new(value)
    }
}

impl<T: Copy> From<&T> for ValueWalker<T> {
    #[inline(always)]
    fn from(value: &T) -> Self {
        Self::new(*value)
    }
}

impl<'ctx, T: Send + Sync + 'static, E: Effect> crate::Walker<'ctx, E> for ValueWalker<T> {
    type Error = Never;

    type Output = ();

    #[inline(always)]
    fn walk<'b: 'c, 'c>(
        self,
        visitor: DynVisitor<'b, 'ctx>,
    ) -> ErasedEffective<'c, Result<Self::Output, Self::Error>, E> {
        // Attempt to visit using the value protocol.
        visit_value::<_, E>(visitor, OwnedStatic(self.0)).map(|_| Ok(()))
    }
}

/// Borrowed form of [`ValueWalker`].
///
/// This walker supports values borrowed for `'ctx` or longer.
pub struct BorrowWalker<'ctx, T: ?Sized>(&'ctx T);

impl<'ctx, T: ?Sized> BorrowWalker<'ctx, T> {
    /// Create walker from a value.
    #[inline(always)]
    pub fn new(value: &'ctx T) -> Self {
        Self(value)
    }
}

impl<'ctx, T: ?Sized + Send + Sync + 'static, E: Effect> crate::Walker<'ctx, E>
    for BorrowWalker<'ctx, T>
{
    type Error = Never;

    type Output = &'ctx T;

    #[inline(always)]
    fn walk<'b: 'c, 'c>(
        self,
        visitor: DynVisitor<'b, 'ctx>,
    ) -> ErasedEffective<'c, Result<Self::Output, Self::Error>, E> {
        // Attempt to visit using the value protocol.
        E::as_ctx((self, visitor), |(this, visitor)| {
            visit_value::<_, E>(visitor.cast(), BorrowedStatic(this.0))
                .map(VisitResult::unit_skipped)
                .cast()
        })
        .if_skipped(|(this, visitor)| {
            visit_value::<_, E>(visitor.cast(), TempBorrowedStatic(this.0))
                .map(VisitResult::unit_skipped)
                .cast()
        })
        .map(|((this, _), _)| Ok(this.0))
    }
}