[yuchdev]

Summary

Rewrite the enums chapter in the narrative technical-literature format used in Chapters 01–06, covering classic unscoped enums through C++26 static reflection.

Correctness fixes

• Explain the distinct enum value range vs underlying representation, including undefined out-of-range conversions for non-fixed enums (CWG 1766).
• Correct C++11 scoped enum default underlying type (int) and completeness of opaque enum declarations.
• Update two existing example programs so that the chapter's code does not demonstrate undefined behavior as though it were harmless.

Expanded coverage

• C++98 unscoped enums, integral promotion and overload resolution.
• C++11 scoped/fixed-underlying enums, opaque declarations, value ranges, ABI.
• C++17 direct-list initialization, C++20 using enum, C++23 std::to_underlying and std::is_scoped_enum.
• Bitmask correctness, switch exhaustiveness, protocol validation, serialization, C interoperability, and enum state transitions.
• C++26 static reflection via std::meta::enumerators_of with availability caveats.
• Five standardized closing sections: rules, diagnostics, standards timeline, Java/Python/C# migration, and further reading.

Scope and validation

Changes only Chapter 07 README and two directly associated examples. Structurally checked the required ending order and code-fence balance. C++26 reflection example is illustrative and uncompiled; CI should validate the repository's C++20 baseline.

[Copilot]

🟡 Changes recommended

Escaped Markdown delimiters break code-example rendering throughout the chapter.

3 open issues

• Escaped Markdown delimiters prevent code blocks and inline code rendering · New
• Documentation describes outdated invalid enum cast demonstration · New
• Incorrectly labels C++14 helper as compatible with C++11 · New

What changed in this PR

Rewrites Chapter 07 as a narrative guide to enums from C++98 through C++26, connecting language rules to the course’s examples.

Changes:

• Expands coverage of conversions, validation, bitmasks, ABI, and reflection.
• Replaces an undefined conversion with a safe unnamed-value example.
• Corrects opaque-enum completeness explanations and adds a compile-time assertion.

File	Description
01_low_level/​07_enums/​README.md	Rewrites and expands the enums chapter.
01_low_level/​07_enums/​02_enums_scoped/​enums_scoped.cpp	Corrects completeness comments and asserts enum size.
01_low_level/​07_enums/​01_enums_core/​enums_core.cpp	Demonstrates a safe, in-range unnamed enum value.

_{Review effort: Balanced}

[Copilot]

Removed the backslashes from the Markdown code and inline-code delimiters and repaired the enum class delimiter. Commit: 502defd.

[Copilot]

Updated the paragraph to describe the in-range unnamed value 3 in the corrected example and noted that the out-of-range cast remains only in a warning comment. Commit: 502defd.