Replace the operator==/!= with operator<=>

[grhoten]

Prior to C++20, you would have to define all comparison operators manually. This is easier to achieve with the 3 way comparison operator. Consider modernizing the C++ comparison operators.

[FrankYFTang]

I look at the document, if the <=> operator is default, then the compiler can automatically generate
operator==, !=, >, <, >=, <= from it.
However, if we define custom <=> operator, the compiler can automatically generate only
operator >, <, >=, <= from it but not ==, !=.
we still need to declare+implement operator== based on <=> then the compiler will generate operator !=

Here is one example of such change. Is that what you have in mind?

diff --git a/inflection/src/inflection/dialog/SemanticFeature.hpp b/inflection/src/inflection/dialog/SemanticFeature.hpp
index ead87c6..614fce0 100644
--- a/inflection/src/inflection/dialog/SemanticFeature.hpp
+++ b/inflection/src/inflection/dialog/SemanticFeature.hpp
@@ -64,7 +64,7 @@ public:
      */
     virtual const ::std::set<::std::u16string>& getBoundedValues() const;
     virtual bool isAliased() const;
-    bool operator<(const SemanticFeature& other) const;
+    std::weak_ordering operator<=>(const SemanticFeature& other) const;
     bool operator==(const SemanticFeature& other) const;
 
     SemanticFeature(const ::std::u16string& name, Type type, const ::std::set<::std::u16string>& boundedValues, bool aliased);

--- a/inflection/src/inflection/dialog/SemanticFeature.cpp
+++ b/inflection/src/inflection/dialog/SemanticFeature.cpp
@@ -72,14 +72,14 @@ bool SemanticFeature::isAliased() const
     return aliased;
 }
 
-bool SemanticFeature::operator<(const SemanticFeature& other) const
+std::weak_ordering SemanticFeature::operator<=>(const SemanticFeature& other) const
 {
-    return name < other.name;
+    return name <=> other.name;
 }
 
 bool SemanticFeature::operator==(const SemanticFeature& other) const
 {
-    return name == other.name;
+    return (*this <=> other) == 0;
 }
 
 } // namespace inflection::dialog

[FrankYFTang]

@grhoten Are changes in the shape as above what you have in mind? I do not believe there is a way to remove the implementaiton of operator== unless operator<=> is = default;

[FrankYFTang]

From #160 I found implementing <=> operator save not too much since we still have to implement == operator if <=> operator is not "= default". We also think requiring C++20 may cause us some issue.

[FrankYFTang]

Dear Rich and George Nebojša and I have some second thoughts after I try to address this issue in #160 . I have the code but 1. it does NOT save the implementation of == operator (read ) 2. we will have internal issues of requiring C++20 , we would like to keep it up to only C++17 for now. Regards, Frank

…

On Mon, Jul 7, 2025 at 10:25 PM George Rhoten ***@***.***> wrote: *grhoten* created an issue (unicode-org/inflection#155) <#155> Prior to C++20, you would have to define all comparison operators manually. This is easier to achieve with the 3 way comparison operator. Consider modernizing the C++ comparison operators. — Reply to this email directly, view it on GitHub <#155>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AJ2N2KNDVLL4PRLG7NXXDED3HNI47AVCNFSM6AAAAACBAB56JGVHI2DSMVQWIX3LMV43ASLTON2WKOZTGIYTCMBXG43DKNI> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

-- Frank Yung-Fong Tang 譚永鋒 / 🌭🍊 Sr. Software Engineer

[grhoten]

This codebase currently uses C++20 very heavily. Your stance is that your potential usage of the API requires C++17, right?

[FrankYFTang]

ok, I try with the following

CC=clang CXX=clang++ ICU_ROOT=/usr/local/google/home/ftang/icu/install CMAKE_CXX_STANDARD=17 cmake --build . -t check -j

It build and run test without any issue. after I added -v I found CMAKE_CXX_STANDARD env has no impact and after I change that from the file to 17 it won't build. So yea, I think we need C++20 regareless.

[grhoten]

C++20 is a 5 year old standard. Though I think the header check in this project forces the API to check for C++14 compatibility, which is older than what ICU supports. That check should likely change.

Since this is a new project, I lean towards not worrying about older versions, unless there is a compelling reason to support older versions. Do you need C++17 support in the API?