treaty -


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use core::fmt::{Debug, Display};
pub mod builders;

use effectful::{bound::SsBound, effective::Canonical, environment::Environment, DynBind};

use crate::protocol::AsVisitor;

/// The canonical builders for a type.
///
/// This trait associates a set of builders with the type.
/// This trait is mainly used by the derive macros to automatically select a builder
/// for a field or variant.
///
/// There can be one canonical builder per mode. The mode is specified by the `M` generic and
/// can be any type. It is only used as a type level tag.
pub trait Build<'src, M, E: Environment>: Sized {
    /// The canonical builder for mode `M`.
    ///
    /// This builder will build values of type `Self`.
    type Builder: Builder<'src, E, Value = Self>;
}

pub trait BuilderTypes<C: SsBound> {
    type Seed: DynBind<C>;

    /// Error that can happen during filling the builder with data.
    type Error: DynBind<C> + Debug + Display;

    type Output: DynBind<C>;

    /// Type to be built.
    type Value;

    fn unwrap_output(output: Self::Output) -> Self::Value;
}

/// Builder for a type.
///
/// The `'ctx` lifetime is some lifetime that is longer than the walker.
/// As such, the built value can borrow from other data with a `'ctx` lifetimes.
///
/// A builder allows creating a value of a type [`Self::Value`][BuilderTypes::Value].
/// The way to use a builder is as follows.
/// - Call [`Default::default()`] to create an instance of the builder.
/// - Call [`Self::as_visitor()`] and give it to a walker's
///     [`walk()`][crate::walk::Walker::walk]. The walker will then fill
///     the builder with data from it's walk.
/// - Call [`Self::build()`] to finish building the value and get any errors
///     that happened during filling it with data.
pub trait Builder<'src, E: Environment>:
    DynBind<E> + AsVisitor<'src, E> + BuilderTypes<E> + Sized
{
    fn from_seed<'u>(seed: Self::Seed) -> Canonical<'u, Self, E>
    where
        Self: 'u;

    /// Finish the value.
    ///
    /// If an error happened with the builder during the walk
    /// it will be reported here.
    fn build<'u>(self) -> Canonical<'u, Result<Self::Output, Self::Error>, E>
    where
        Self: 'u;
}