[libcxx-commits] [libcxx] [libc++] Remove [[nodiscard]] from map etc. operator[] (PR #172444)

[Hans Wennborg via libcxx-commits]

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@@ -465,13 +465,13 @@ class flat_map {
   }
 
   // [flat.map.access], element access
-  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](const key_type& __x)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](const key_type& __x)
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zmodem wrote:

It sounds like we're on the same page about `map` and `unordered_map`.

I don't feel particularly strongly about `flat_map` since we don't have many uses, but I think we should strive for consistency between the interfaces.

https://libcxx.llvm.org/CodingGuidelines.html#apply-nodiscard-where-relevant says nodiscard should be used

> where discarding the return value is most likely a correctness issue. For example a locking constructor in `unique_lock.`

I don't think nodiscard on these `operator[]`'s meets the criterion of "most likely a correctness issue". Of the instances I've seen so far, none have been a correctness issue. Do you have any data that suggests otherwise?

https://github.com/llvm/llvm-project/pull/172444