[PATCH] D132232: Update coding standards for constexpr if statements; NFC

[Erich Keane via Phabricator via llvm-commits]

erichkeane added a comment.

Agreed.  For other reviewers, note that this is the compelling example:

  template<typename T>
  static constexpr bool VarTempl = true;
  
  template<typename T>
  int func() {
    if constexpr (VarTempl<T>)
      return 1;
    
    static_assert(!VarTempl<T>);
  }
  
  void use() {
      func<int>();
  }

The static-assert would fail, since it isn't a discarded statement.

  template<typename T>
  static constexpr bool VarTempl = true;
  
  template<typename T>
  int func() {
    if constexpr (VarTempl<T>)
      return 1;
    else 
    static_assert(!VarTempl<T>);
  }
  
  void use() {
      func<int>();
  }

But in THIS case the static-assert is discarded. That is, the 'else' in a if-constexpr isn't required to be anything other than lexically valid, so dependent lookup doesn't need to happen, instantiations aren't required, etc.

Therefore there is EXTREME value to having an 'else' there after a return.


Repository:
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  https://reviews.llvm.org/D132232/new/

https://reviews.llvm.org/D132232