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Author: Sophomore42

_CppCon/2017/runtime_polymorphism_back_to_basics.md

@@ -0,0 +1,81 @@
+---
+title: Runtime Polymorphism: Back to Basics by Louis Dionne
+date: 2024-10-14
+url: https://www.bilibili.com/video/BV1Vx411V7Rd?p=137
+---
+
+problems:
+
+- returning related types from a function
+- storing related types in a container
+
+variant sometimes does the trick
+
+- but it only works for closed set of types
+- using visitation is sometimes not convenient
+
+bottom line: manipulating an open set of related types with different representations
+
+inheritance has many problems:
+
+- bakes in reference semantics
+- heap allocations
+- bakes in nullable semantics
+- ownership hell
+- doesn't play well with algorithms
+- intrusive
+
+ref: [Sean Parent](https://youtu.be/QGcVXgEVMJg)
+
+Goal: independent storage and method dispatch
+
+- Storage policy
+  - Remote Storage(Just like using dyno::remote_storage)
+  - The Small Buffer Optimization: Add a buffer in the type
+  - Always-Local Storage: may failed
+  - Non-Owning storage
+  - Shared Remote Storage
+- VTable policy
+  - Remote
+  - Inline: Pessimization
+  - Partial Vtable Inlining
+
+Remote Storage: strengths and weaknesses
+
+- simple model, similar to classic inheritance
+- Always requires an allocation
+
+The Small Buffer Optimization: strengths and weakness
+
+- does not always require allocating
+- takes up more space
+- Copy/move/swap is more complicated
+- Dispatching may be more costly
+
+Always-Local Storage: strengths and weakness
+
+- No allocation ever
+- Simple dispatching
+- Takes up more space
+
+GuideLines
+
+- use local storage whenever you can afford it
+- otherwise, use SBO with the largest reasonable size
+- Use purely-remote storage only when object sizes are so scattered SBO wouldn't help
+- By default, all methods are in the remote vtable
+- Consider inlining some methods if
+  - you have slack space
+  - you know you're calling them often
+  - you've measured it makes a difference
+
+Summary
+
+- Inheritance is only a choice of run time polymorphism
+- Many ways of storing polymorphic objects
+- Vtable can be inlined
+- Type erasure is tedious to do manually
+
+ref: dyno lib
+
+ref: Zack Laine's CppCon 2014 talk

_CppCon/2020/dynamic_polymorphism_with_metaclasses_and_code_injection.md

@@ -6,7 +6,7 @@ url: https://www.bilibili.com/video/BV1YA411J7Pe?p=38
 
 Polymorphism:The provision of a single interface to entities of different types.
 
-ref: Runtime Polymorphism: Back to Basics
+ref: Runtime Polymorphism: Back to Basics[markdown](../2017/runtime_polymorphism_back_to_basics.md) [html](../2017/runtime_polymorphism_back_to_basics.html)
 
 ref: Inheritance is the base class of evil