Should YAML::detail::iterator_value really be part of the detail namespace? (Support for C++20 ranges)

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
25/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
cpp
Domain
api

Research direction

The question is whether YAML::detail::iterator_value, which the reproducer in the issue uses directly, should be promoted to public API so that YAML::Node works with C++20 ranges such as std::ranges::all_of. Start by finding where that type is declared and how YAML::Node's iterator exposes its value type, then compare with the iterator-based loop in the wiki. Done means a maintainer has decided on the public type name and its exposure, and the change is covered by a test that iterates a node with a range algorithm.

Written by the indexing model from the issue text.

Description

A yaml node technically satisfies the the requirements for a range - however, the range value type of a YAML::Node is not technically part of the public interface of yaml-cpp. Consider the following example

#include <cstdlib>
#include <string_view>

#include <algorithm>
#include <cstring>
#include <iostream>

#include <yaml-cpp/yaml.h>

constexpr std::string_view SRC =
    "scrambled-eggs:\n"
    "  ingredient.egg: 2\n"
    "  ingredient.butter: 1 tbsp\n"
    "  ingredient.salt: 1 pinch";

bool IsIngredient(const std::string_view Path)
{
    return std::strstr(Path.data(), "ingredient.") != nullptr;
}

bool IsValid(const YAML::detail::iterator_value & Value)
{
    return IsIngredient(Value.first.Scalar());
}

int main()
{
    const YAML::Node Src = YAML::Load(SRC.data());
    const YAML::Node RecipeConfig = Src["scrambled-eggs"];

    const bool AllValid = std::ranges::all_of(RecipeConfig, IsValid);
    std::cout << "All valid ingredients? " << (AllValid? "Yes" : "No") << "\n";
    return EXIT_SUCCESS;
}

This is prefectly valid C++20 code - it compiles and outputs All valid ingredients? Yes. However, you might argue that this isn't perfectly valid yaml-cpp code, since it uses an internal data type YAML::detail::iterator_value which I don't think is part of the public API? However, this code is much more concise, and - at the risk of sounding subjective - I would also argue much more legible than the equivalent code using an iterator-based for-loop as suggested in the wiki pages.

So I guess the point of this post is to make a request that the iterator value of a YAML::Node should be part of the public API and not be an internal detail.

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