C+ + Parent-Child Data Passing in Recursive Lambda Functions

Learn how to efficiently pass data from parent to child in C+ + using recursive lambda functions and achieve the desired output when iterating over data structures.
---
This video is based on the question https://stackoverflow.com/q/71414888/ asked by the user 'VL3DGA' ( https://stackoverflow.com/u/18421951/ ) and on the answer https://stackoverflow.com/a/71415981/ provided by the user 'jwezorek' ( https://stackoverflow.com/u/1413244/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: C+ + : How to pass data from parent to child in a lambda inside a recursive function

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/licensing
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/by-sa/4.0/ ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
C+ + Parent-Child Data Passing in Recursive Lambda Functions

In the world of C+ + , passing data efficiently between functions can be a challenging task, especially when dealing with recursive functions and lambda expressions. A common scenario is the need to iterate over a data structure and collect specific paths of its elements, while ensuring that this process remains as generic and reusable as possible. In this guide, we will explore how to accomplish this task, highlighting a typical problem and offering a detailed solution.

The Problem: Collecting Paths in a Recursive Structure

When iterating over a nested data structure, you may encounter a situation where you want to capture hierarchical paths of each element. Let's say you have the following desired output for a tree-like hierarchy:

[[See Video to Reveal this Text or Code Snippet]]

However, your current implementation yields:

[[See Video to Reveal this Text or Code Snippet]]

This deviation arises due to how the paths are constructed and modified as the recursion moves through the structural hierarchy. The challenge at hand is to adjust the recursive function so it passes and updates paths correctly.

Key Observations

Passing by Reference vs by Value: Using string& fullPath causes continued stacking of paths, while string fullPath resets it to an empty string during each recursion, leading to incorrect results.

Avoiding Data Structure Modifications: We cannot alter the original data tree structure to append additional information for path tracking.

Decoupling Logic: We want a cleaner method that decouples the logic of path assignment from the recursive method calls.

The Solution: Using Pre- and Post-Visit Functors

To solve the issue effectively, we can introduce pre- and post-visit operations within our recursive function. By doing this, we can manipulate the path before and after traversing child nodes without interfering with the core recursive logic.

Implementation Steps

Define the Recursive Function: This function will accept two functors—one for pre-visit actions that update the path, and another for post-visit actions to manipulate the path once child exploration is complete.

Construct the Functors: The pre-visit functor will build the path string, while the post-visit will help in "popping" the last element off the path after the children are fully processed.

Code Example

Here’s how the complete implementation might look:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of Key Components

MyElement Class: Represents elements of the data structure with a name and children.

WithAllMembersRecursively Function: This function recursively calls itself while modifying and restoring the path string at key moments.

Main Function: Sets up the hierarchy, calls the recursive function, and outputs the paths.

Conclusion

Passing data effectively between parent and child elements in recursive structures can be achieved with clever use of pre- and post-visit functors in C+ + . By breaking down the complexity of the recursion and isolating the path management, we can maintain a clear and efficient implementation that is generic enough for various data structures. This strategy not only resolves the immediate challenge but also opens the door for future enhancements and simpler modifications.

Feel free to experiment with these concepts in your own C+ + projects and witness the cleaner results in your recursive data handling tasks!

Видео C+ + Parent-Child Data Passing in Recursive Lambda Functions канала vlogize