1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147

#![allow(dead_code)]

//! Module defining DependentRc, a wrapper around the Rc type.
//!
//! This module both defines the `DependentRc` struct, as well as the corresponding `to_view!` macro, which can be used to obtain views from an instance of `DependentRc`.
//!


use super::push_ref;

use std::rc::Rc;
use std::convert::*;
use std::any::Any;
use std::mem::transmute;
use std::ops::{Deref, DerefMut};


/// Macro for obtaining views from DependentRc
///
/// # Error
/// It is a compile time error to use this macro to produce a view for a trait that the underlying struct does not implement.
/// 
/// # Examples
///
/// ```
/// # use std::rc::Weak;
/// # #[macro_use] extern crate dependent_view;
/// # use dependent_view::rc::DependentRc;
/// struct ExampleStruct {
///    // arbitrary fields
/// # id: usize
/// }
/// trait ExampleTrait {
///   fn example_method(&self);
/// }
/// # impl ExampleStruct { fn new() -> Self { ExampleStruct {id: 0}}}
/// impl ExampleTrait for ExampleStruct {
/// #        fn example_method(&self) {
///              // some implementation...
/// #            println!("id: {:?}", self.id);
/// #          }
/// }
/// # fn main() {
/// let mut item : DependentRc<ExampleStruct> = DependentRc::new(ExampleStruct::new());
/// let view : Weak<ExampleTrait> = to_view!(item);
/// # }
/// ```
#[macro_export]
macro_rules! to_view {
    ($dep:tt) => {
        (unsafe { $dep.into_view_internal::<_, _,_, _, _>(|item| item.clone() as ::std::rc::Rc<_>, |item| ::std::rc::Rc::downgrade(item), |item| unsafe { ::std::mem::transmute(item) })});
    }
}



/// `DependentRc<T>` is a simple wrapper around the `Rc<T>`  type, imbuing it with the capability to provide "views" (`Weak<Trait>`) of non-owned structs to separate components of a system. 
///
/// Internally, it does this by retaining an `Rc<Trait>` for each view you make - thus when the
/// `DependentRc` is dropped, all of the weak references are automatically invalidated.
pub struct DependentRc<T> {
    item: Rc<T>,
    dependants: Vec<Rc<Any>>
}



impl<T> DependentRc<T> {
    /// Constructs a `DependentRc` by wrapping an underlying type
    pub fn new(item: T) -> DependentRc<T> {
        DependentRc {
            item: Rc::new(item),
            dependants: Vec::new()
        }
    }

    /// internal hidden function used to produce a Weak reference
    /// # Warn
    /// This function should only be called through the `to_view!` macro. It is not intended for direct use.
    /// # Remarks
    /// This struct works by cloning the underlying Rc, using the fact that when cloning, it is possible
    /// to upcast an `Rc<Concrete>` to an `Rc<Trait>`.
    /// From this point, the `Rc<Trait>` is transmuted into an `Rc<Any>`. While this is an unsafe,
    /// unchecked cast, we just want to keep the on Drop functionality of `Rc<Any>` and don't provide    /// any ways to use the trait, so it shouldn't be a problem
    #[doc(hidden)]
    pub unsafe fn into_view_internal<X,Y,G,F, H>(&mut self, conversion: F, downgrade: G, to_any: H) -> Y
    where F : FnOnce(&Rc<T>) -> X,
          G : FnOnce(&X) -> Y,
          H : FnOnce(X) -> Rc<Any>
    {
        let reference : X = conversion(&self.item);
        let reference : Rc<Any> = to_any(reference);
        let reference : &Rc<Any> = push_ref(&mut self.dependants, reference);
        let reference : &X =  transmute(reference);
        downgrade(reference)
    }
}



impl<T> Deref for DependentRc<T> {
    type Target = Rc<T>;

    fn deref(&self) -> &Rc<T> {
        &self.item
    }
}
impl<T> DerefMut for DependentRc<T> {
    fn deref_mut(&mut self) -> &mut Rc<T> {
        &mut self.item
    }
}


/// Returns a reference to the underlying `Rc` struct
impl<T> AsRef<Rc<T>> for DependentRc<T> {
    fn as_ref(&self) -> &Rc<T> {
        &self.item
    }
}

/// Returns a mutable reference to the underlying `Rc` struct
impl<T> AsMut<Rc<T>> for DependentRc<T> {
    fn as_mut(&mut self) -> &mut Rc<T> {
        &mut self.item
    }
}


/// Constructs a DependentRc from an `Rc`, imbuing it with the capability to produce views.
impl <T> From<Rc<T>> for DependentRc<T> {
    fn from(item: Rc<T>) -> DependentRc<T> {
        DependentRc {
            item,
            dependants: Vec::new()
        }
    }
}

/// Unwraps the `DependentRc`, returning it's internal `Rc`
///
/// Note: This will invalidate all `Weak<Trait>` views you have constructed from this object.
impl <T> Into<Rc<T>> for DependentRc<T> {
    fn into(self) -> Rc<T> {
        self.item
    }
}