Stabilize new naming conventions

[ken-matsui]

Idea

• Files/Directories: PascalCase
• Types/Classes: PascalCase
• Variables: snake_case
• Class (non-struct) Member Variables: snake_case_
• Functions: camelCase
• Class (non-struct) Methods: camelCase_

Reasoning/Explanation

• Variables use snake_case since they tend to be shorter than functions.
• Why not the m prefix?
  • We need to use m_ for snake_case and m for camelCase.
  • m_ and m are inconsistent.
  • m_snake_case is longer than snake_case_.
• Class Members and non-members (and struct members) are distinguished by the _ suffix, which is similar to Google's C++ Coding Style.
  • The difference is that we apply this pattern to methods as well.
• Only class members have the _ suffix because they have methods and within methods, variables/functions and members are hard to be distinguished. (Structs won't have methods. => this is different from Google's)

Steps to apply this new policy

1. Apply Class vs Struct style.
2. Apply the new Class (non-struct) Methods naming convention.
3. Apply the new Class (non-struct) Member Variables naming convention.
4. Apply the new Variables naming convention.

See also

• https://github.com/poac-dev/poac/blob/bca4bbde7c9eaea9245e53807d49c322583bf187/CONTRIBUTING.md#naming-conventions-under-construction
• build: support lib.cc #1035 (comment)
• https://llvm.org/docs/CodingStandards.html#name-types-functions-variables-and-enumerators-properly
• https://llvm.org/docs/Proposals/VariableNames.html