cursive/src/view/any.rs

use crate::view::View;
use std::any::Any;

/// A view that can be downcasted to its concrete type.
///
/// This trait is automatically implemented for any `T: View`.
pub trait AnyView {
    /// Downcast self to a `Any`.
    fn as_any(&self) -> &dyn Any;

    /// Downcast self to a mutable `Any`.
    fn as_any_mut(&mut self) -> &mut dyn Any;

    /// Returns a boxed any from a boxed self.
    ///
    /// Can be used before `Box::downcast()`.
    ///
    /// # Examples
    ///
    /// ```rust
    /// # use cursive::views::TextView;
    /// # use cursive::view::View;
    /// # fn main() {
    /// let boxed: Box<View> = Box::new(TextView::new("text"));
    /// let text: Box<TextView> = boxed.as_boxed_any().downcast().unwrap();
    /// # }
    /// ```
    fn as_boxed_any(self: Box<Self>) -> Box<dyn Any>;
}

impl<T: View> AnyView for T {
    /// Downcast self to a `Any`.
    fn as_any(&self) -> &dyn Any {
        self
    }

    /// Downcast self to a mutable `Any`.
    fn as_any_mut(&mut self) -> &mut dyn Any {
        self
    }

    fn as_boxed_any(self: Box<Self>) -> Box<dyn Any> {
        self
    }
}

impl dyn AnyView {
    /// Attempts to downcast `self` to a concrete type.
    pub fn downcast_ref<T: Any>(&self) -> Option<&T> {
        self.as_any().downcast_ref()
    }

    /// Attempts to downcast `self` to a concrete type.
    pub fn downcast_mut<T: Any>(&mut self) -> Option<&mut T> {
        self.as_any_mut().downcast_mut()
    }

    /// Attempts to downcast `Box<Self>` to a concrete type.
    pub fn downcast<T: Any>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
        // Do the check here + unwrap, so the error
        // value is `Self` and not `dyn Any`.
        if self.as_any().is::<T>() {
            Ok(self.as_boxed_any().downcast().unwrap())
        } else {
            Err(self)
        }
    }
}