Remove using namespace std / using-declarations from headers

[zzcgumn]

What

using namespace std; (and one namespace-scope using std::chrono::time_point;) appeared at file scope in several headers. That injects names into every translation unit that includes the header, directly or transitively — bad style and a maintenance hazard.

Headers cleaned (declarations now fully qualified)

• library/src/system/system.hpp
• library/src/system/thread_mgr.hpp
• library/src/system/time_stat.hpp
• library/src/system/timer.hpp
• library/tests/TestTimer.hpp

The using Clock = std::chrono::steady_clock; alias-declarations are left as-is (they are type aliases, not using-directives/declarations).

Translation units updated

Several .cpp files had been leaning on those headers' transitive using. They now declare what they need locally:

• Specific using std::...; declarations added to init.cpp and the system/*.cpp printing/formatting code.
• Point qualification (std::vector, std::chrono::time_point) in calc_tables.cpp, solve_board.cpp, timer.cpp, TestTimer.cpp.
• testcommon.cpp gains using std::left; using std::right; alongside its existing using std:: block.

Coding standard

.github/instructions/cpp.instructions.md gains a dedicated Namespace using section replacing the terse "No using namespace in headers" bullet: headers ban namespace-scope using-directives and using-declarations (class/function-body using and alias-declarations still fine); .cpp files prefer specific using-declarations, with file-scope using namespace permitted but discouraged; never rely on a using supplied by an included header.

Testing

• bazel build //... — passes
• bazel test //... — 93/93 pass

🤖 Generated with Claude Code

Closes #357

[Copilot]

🟡 Changes recommended

library/src/system/timer.hpp uses clock_t but does not include <ctime>, which can break header self-containment/portability across standard libraries.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR removes header-level namespace pollution by eliminating using namespace std; and namespace-scope using X::name; from several headers, then updating call sites and the C++ style guide to prevent recurrence.

Changes:

• Fully qualified standard-library types in affected headers (e.g., std::string, std::vector, std::chrono::time_point).
• Updated translation units/tests that previously relied on transitive using from headers by adding local using std::...; or explicit std:: qualification.
• Expanded .github/instructions/cpp.instructions.md with a dedicated “Namespace using” section clarifying header vs .cpp rules.

File summaries

File	Description
library/src/system/system.hpp	Removes header using namespace std; and qualifies STL usage in declarations.
library/src/system/thread_mgr.hpp	Removes header using namespace std; and qualifies std::vector/std::string.
library/src/system/time_stat.hpp	Removes header using namespace std; and qualifies std::string return types.
library/src/system/timer.hpp	Removes header using namespace std; / using std::chrono::time_point; and qualifies std::string/std::chrono::time_point.
library/tests/TestTimer.hpp	Removes namespace-scope using std::chrono::time_point; and fully qualifies std::chrono::time_point.
library/src/init.cpp	Adds local using std::...; declarations to avoid relying on header-provided using.
library/src/solve_board.cpp	Qualifies std::vector in helper signature to avoid transitive using.
library/src/calc_tables.cpp	Qualifies std::vector in helper signature to avoid transitive using.
library/src/system/system.cpp	Adds local using std::...; declarations for formatting/containers used in the TU.
library/src/system/thread_mgr.cpp	Adds local using std::...; declarations used by output/formatting code.
library/src/system/time_stat.cpp	Adds local using std::...; declarations used by formatting code.
library/src/system/time_stat_list.cpp	Adds local using std::...; declarations used by formatting code.
library/src/system/timer.cpp	Adds local using std::...; declarations and qualifies chrono types where needed.
library/src/system/timer_group.cpp	Adds local using std::...; declarations used by formatting/string building.
library/src/system/timer_list.cpp	Adds local using std::...; declarations used by printing code.
library/tests/TestTimer.cpp	Qualifies std::chrono::time_point in end() to avoid relying on header using.
library/tests/testcommon.cpp	Adds using std::left/right; alongside existing local using block.
.github/instructions/cpp.instructions.md	Documents the “Namespace using” policy in detail.

Review details

• Files reviewed: 18/18 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🟢 Approval recommended

The changes consistently remove header-level namespace pollution while updating dependent translation units accordingly, and the updates are low-risk and stylistically aligned with the documented conventions.

Review details

• Files reviewed: 18/18 changed files
• Comments generated: 0 new
• Review effort level: Lite

[krtschil]

Good to go

[Copilot]

🔵 Needs a closer look

A few headers/translation units still rely on unqualified clock_t/clock() (not guaranteed outside std::), which can cause non-portable compile failures after removing header-level using.

Review details

Suppressed comments (5)

Previously missed (5) — in code that hasn't changed since the last review.

library/tests/TestTimer.cpp:97

• Use std::clock_t / std::clock() consistently in this block as well (and update the static_cast type) to avoid depending on a global clock_t name.

  std::chrono::time_point<Clock> user1 = Clock::now();
  clock_t sys1 = clock();

  duration<double, std::milli> d = user1 - user0_;
  const long tuser = static_cast<long>(d.count());

library/src/system/timer.cpp:66

• Prefer std::clock_t/std::clock() here so this .cpp does not rely on a global clock_t or clock() being injected via C headers; this becomes more important after removing transitive using from headers.
  library/src/system/timer.hpp:38
• After removing header-level using namespace std, clock_t should be qualified as std::clock_t for standard compliance; <ctime> only guarantees std::clock_t, not a global clock_t typedef on all platforms.
  library/tests/TestTimer.cpp:93
• This file now avoids relying on transitive using from headers; clock_t and clock() should be written as std::clock_t / std::clock() for standard compliance (including <ctime> only guarantees these names in std::).
  library/tests/TestTimer.hpp:47
• This header now avoids namespace-scope using declarations; clock_t should similarly be written as std::clock_t because <ctime> only guarantees the typedef in std::, not necessarily in the global namespace.

• Files reviewed: 19/19 changed files
• Comments generated: 0 new
• Review effort level: Lite

[Copilot]

🟢 Approval recommended

The changes consistently remove header-level namespace pollution and update dependent translation units accordingly without introducing API/behavior changes.

Review details

• Files reviewed: 20/20 changed files
• Comments generated: 0 new
• Review effort level: Lite