std::stodの代わりにstd::from_charsを使用する

[smdn]

Description

文字列から数値への変換において、std::stodの代わりにstd::from_charsを使用する。
これによって、例外ハンドリングの必要がない実装に簡略化する。

同時に、引数の型をstd::stringからstd::string_viewに変える。

ただし、GitHub Actions macOSランナーイメージのデフォルトのツールセットでは、まだstd::from_charsがdoubleへの変換をサポートしていないようなので、サポートされ次第マージする。

Considerations

以下のように、まだstd::from_charsがサポートされていないので、デフォルトのツールセットでコンパイルできるようになるまでマージを控える。

Run tests with an implementation of C++ (GitHub Actions, make + G++) ...
Apple clang version 17.0.0 (clang-1700.0.13.5)
Target: arm64-apple-darwin24.6.0
Thread model: posix
InstalledDir: /Applications/Xcode_16.4.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
g++ -std=c++2a -O2 -Wall -c polish.cpp
polish.cpp:398:39: error: call to deleted function 'from_chars'
  398 |     [[maybe_unused]] auto [ptr, ec] = std::from_chars(
      |                                       ^~~~~~~~~~~~~~~
/Applications/Xcode_16.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__charconv/from_chars_integral.h:38:19: note: candidate function has been explicitly deleted
   38 | from_chars_result from_chars(const char*, const char*, bool, int = 10) = delete;
      |                   ^
/Applications/Xcode_16.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__charconv/from_chars_integral.h:224:1: note: candidate template ignored: requirement 'is_integral<double>::value' was not satisfied [with _Tp = double]
  224 | from_chars(const char* __first, const char* __last, _Tp& __value) {
      | ^
/Applications/Xcode_16.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__charconv/from_chars_integral.h:230:1: note: candidate function template not viable: requires 4 arguments, but 3 were provided
  230 | from_chars(const char* __first, const char* __last, _Tp& __value, int __base) {
      | ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
make: *** [polish.o] Error 1

Run tests with an implementation of C++ (GitHub Actions, make + Clang) ...
Apple clang version 17.0.0 (clang-1700.0.13.5)
Target: arm64-apple-darwin24.6.0
Thread model: posix
InstalledDir: /Applications/Xcode_16.4.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
clang++ -std=c++2a -O2 -Wall -c polish.cpp
polish.cpp:398:39: error: call to deleted function 'from_chars'
  398 |     [[maybe_unused]] auto [ptr, ec] = std::from_chars(
      |                                       ^~~~~~~~~~~~~~~
/Applications/Xcode_16.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__charconv/from_chars_integral.h:38:19: note: candidate function has been explicitly deleted
   38 | from_chars_result from_chars(const char*, const char*, bool, int = 10) = delete;
      |                   ^
/Applications/Xcode_16.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__charconv/from_chars_integral.h:224:1: note: candidate template ignored: requirement 'is_integral<double>::value' was not satisfied [with _Tp = double]
  224 | from_chars(const char* __first, const char* __last, _Tp& __value) {
      | ^
/Applications/Xcode_16.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__charconv/from_chars_integral.h:230:1: note: candidate function template not viable: requires 4 arguments, but 3 were provided
  230 | from_chars(const char* __first, const char* __last, _Tp& __value, int __base) {
      | ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.
make: *** [polish.o] Error 1

Operating System
  macOS
  15.7.3
  24G419
Runner Image
  Image: macos-15-arm64
  Version: 20260105.0094.1
  Included Software: https://github.com/actions/runner-images/blob/macos-15-arm64/20260105.0094/images/macos/macos-15-arm64-Readme.md
  Image Release: https://github.com/actions/runner-images/releases/tag/macos-15-arm64%2F20260105.0094