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Author: Sophomore42

_code/CppCon/2023/thinking_functionally _in_c++.md

@@ -4,4 +4,71 @@ date: 2024-10-29
 url: https://www.bilibili.com/video/BV1BC4y1R7iL?p=19
 ---
 
+A different ways of thinking about a problem
+
+ref: The forgotten functional pattern by Ben Deane for deeply functional topic
+
+Paradigms:
+
+- Imperative or Procedual: roots with c
+- Object Oriented: roots with simula
+- Functional: STL, Lambdas, Ranges
+
+## Identifying code functionally
+
+Functional Code Categories:
+
+- Actions: Depend on when or how many times they are called. Observable changes occur.
+- Calculation: Depend only on their inputs and not when or how they are called. Calling them with the same inputs always results in the same outputs. No observable changes occur.
+- Data: Unchanging records od events. Used as input to calculations and actions. Records the results of calculations adn actions.
+
+- Actions
+  - Allow input to programs that is unknown when the program was written
+  - Performing an action has consequences
+  - Affect how a program executes
+- Calculation
+  - Reliable
+  - Encapsulated, has no effect outside of itself
+  - Thread safe, since it is entirely salf contained, no ordering or locking is necessary
+- Data
+  - Fundamental building block
+  - Immutable, data doesn't change
+  - Transparent, you can look at data and see what it is
+  - Open to interpretation, data can mean different things to different components without changing value
+  - Used by calculations and actions to communicate with other calculations and actions
+
+Data is all about context
+
+Breaking down a problem to actions, calculations and data.
+
+std::copy_if
+
+## Functions as Data
+
+Passing functions to functions
+
+Return functions from functions
+
+currying: transform a function of several arguments to a function of a single argument.
+
+RAII
+
+Call C API through the lambda
+
+std::forward
+
+```cpp
+auto Oven = [](auto handle)
+{
+    return [h=handle](auto func, auto&&... args) mutable
+{
+      return func(h,std::forward<decltype(args)>(args)...);
+    }
+}
+```
+
+Creating an object wrapper using a lambda.
+
+## Composable Functions
+