//! Provides [`Decode`] for decoding values from the database.
use crate;
use crate BoxDynError;
use crate ValueRef;
/// A type that can be decoded from the database.
///
/// ## How can I implement `Decode`?
///
/// A manual implementation of `Decode` can be useful when adding support for
/// types externally to SQLx.
///
/// The following showcases how to implement `Decode` to be generic over [`Database`]. The
/// implementation can be marginally simpler if you remove the `DB` type parameter and explicitly
/// use the concrete [`ValueRef`](HasValueRef::ValueRef) and [`TypeInfo`](Database::TypeInfo) types.
///
/// ```rust
/// # use sqlx_core::database::{Database, HasValueRef};
/// # use sqlx_core::decode::Decode;
/// # use sqlx_core::types::Type;
/// # use std::error::Error;
/// #
/// struct MyType;
///
/// # impl<DB: Database> Type<DB> for MyType {
/// # fn type_info() -> DB::TypeInfo { todo!() }
/// # }
/// #
/// # impl std::str::FromStr for MyType {
/// # type Err = sqlx_core::error::Error;
/// # fn from_str(s: &str) -> Result<Self, Self::Err> { todo!() }
/// # }
/// #
/// // DB is the database driver
/// // `'r` is the lifetime of the `Row` being decoded
/// impl<'r, DB: Database> Decode<'r, DB> for MyType
/// where
/// // we want to delegate some of the work to string decoding so let's make sure strings
/// // are supported by the database
/// &'r str: Decode<'r, DB>
/// {
/// fn decode(
/// value: <DB as HasValueRef<'r>>::ValueRef,
/// ) -> Result<MyType, Box<dyn Error + 'static + Send + Sync>> {
/// // the interface of ValueRef is largely unstable at the moment
/// // so this is not directly implementable
///
/// // however, you can delegate to a type that matches the format of the type you want
/// // to decode (such as a UTF-8 string)
///
/// let value = <&str as Decode<DB>>::decode(value)?;
///
/// // now you can parse this into your type (assuming there is a `FromStr`)
///
/// Ok(value.parse()?)
/// }
/// }
/// ```
// implement `Decode` for Option<T> for all SQL types