treaty -


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use crate::{
    any::{BorrowedStatic, OwnedStatic},
    effect::{Effect, Future},
    never::Never,
    protocol::{visitor::visit_value, Visitor},
    WalkerTypes,
};

/// 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.
    pub fn new(value: T) -> Self {
        Self(value)
    }
}

impl<T> From<T> for ValueWalker<T> {
    fn from(value: T) -> Self {
        Self::new(value)
    }
}

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

impl<T> WalkerTypes for ValueWalker<T> {
    type Error = Never;

    type Output = ();
}

impl<'ctx, T: Send + 'static, E: Effect> crate::Walker<'ctx, E> for ValueWalker<T> {
    fn walk<'a>(
        self,
        visitor: Visitor<'a, 'ctx>,
    ) -> Future<'a, Result<Self::Output, Self::Error>, E>
    where
        Self: 'a,
    {
        // Attempt to visit using the value protocol.
        E::map(
            visit_value::<_, E>(visitor, OwnedStatic(self.0)),
            |_| 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.
    pub fn new(value: &'ctx T) -> Self {
        Self(value)
    }
}

impl<'ctx, T: ?Sized> WalkerTypes for BorrowWalker<'ctx, T> {
    type Error = Never;

    type Output = ();
}

impl<'ctx, T: ?Sized + Sync + 'static, E: Effect> crate::Walker<'ctx, E> for BorrowWalker<'ctx, T> {
    fn walk<'a>(
        self,
        visitor: Visitor<'a, 'ctx>,
    ) -> Future<'a, Result<Self::Output, Self::Error>, E>
    where
        Self: 'a,
    {
        // Attempt to visit using the value protocol.
        E::map(visit_value::<_, E>(visitor, BorrowedStatic(self.0)), |_| {
            Ok(())
        })
    }
}