From bb2303a654c08fd295828b3b12e1cfb6daddbc28 Mon Sep 17 00:00:00 2001
From: Nathan Ward <nathansward@comcast.net>
Date: Tue, 30 Aug 2022 21:06:32 +0000
Subject: [PATCH] Add `pop` method for `List` trait. (#5797)

# Objective

- The reflection `List` trait does not have a `pop` function.
- Popping elements off a list is a common use case and is almost always supported by `List`-like types.

## Solution

- Add the `pop()` method to the `List` trait and add the appropriate implementations of this function.

## Migration Guide

- Any custom type that implements the `List` trait will now need to implement the `pop` method.


Co-authored-by: Carter Anderson <mcanders1@gmail.com>
---
 crates/bevy_reflect/src/impls/smallvec.rs | 4 ++++
 crates/bevy_reflect/src/impls/std.rs      | 4 ++++
 crates/bevy_reflect/src/list.rs           | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/crates/bevy_reflect/src/impls/smallvec.rs b/crates/bevy_reflect/src/impls/smallvec.rs
index 918f74d40c..11f3c80012 100644
--- a/crates/bevy_reflect/src/impls/smallvec.rs
+++ b/crates/bevy_reflect/src/impls/smallvec.rs
@@ -54,6 +54,10 @@ where
         });
         SmallVec::push(self, value);
     }
+
+    fn pop(&mut self) -> Option<Box<dyn Reflect>> {
+        self.pop().map(|value| Box::new(value) as Box<dyn Reflect>)
+    }
 }
 
 impl<T: smallvec::Array + Send + Sync + 'static> Reflect for SmallVec<T>
diff --git a/crates/bevy_reflect/src/impls/std.rs b/crates/bevy_reflect/src/impls/std.rs
index b79858d16c..5c48fbabca 100644
--- a/crates/bevy_reflect/src/impls/std.rs
+++ b/crates/bevy_reflect/src/impls/std.rs
@@ -137,6 +137,10 @@ impl<T: FromReflect> List for Vec<T> {
         });
         Vec::push(self, value);
     }
+
+    fn pop(&mut self) -> Option<Box<dyn Reflect>> {
+        self.pop().map(|value| Box::new(value) as Box<dyn Reflect>)
+    }
 }
 
 impl<T: FromReflect> Reflect for Vec<T> {
diff --git a/crates/bevy_reflect/src/list.rs b/crates/bevy_reflect/src/list.rs
index 9e8c0c65f6..26c8840c7f 100644
--- a/crates/bevy_reflect/src/list.rs
+++ b/crates/bevy_reflect/src/list.rs
@@ -15,6 +15,9 @@ pub trait List: Reflect + Array {
     /// Appends an element to the list.
     fn push(&mut self, value: Box<dyn Reflect>);
 
+    /// Removes the last element from the list (highest index in the array) and returns it, or [`None`] if it is empty.
+    fn pop(&mut self) -> Option<Box<dyn Reflect>>;
+
     /// Clones the list, producing a [`DynamicList`].
     fn clone_dynamic(&self) -> DynamicList {
         DynamicList {
@@ -151,6 +154,10 @@ impl List for DynamicList {
         DynamicList::push_box(self, value);
     }
 
+    fn pop(&mut self) -> Option<Box<dyn Reflect>> {
+        self.values.pop()
+    }
+
     fn clone_dynamic(&self) -> DynamicList {
         DynamicList {
             name: self.name.clone(),