Fix build with C++20

Fix compiler error C2666 when building with MSVC.

Refs: simdutf/simdutf@ba2c557

.github/workflows/ubuntu22-cxx20.yml

@@ -0,0 +1,25 @@
+name: Ubuntu 22.04 CI (GCC 11, CXX 20)
+
+on: [push, pull_request]
+
+jobs:
+  ubuntu-build:
+    if: >-
+      ! contains(toJSON(github.event.commits.*.message), '[skip ci]') &&
+      ! contains(toJSON(github.event.commits.*.message), '[skip github]')
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - name: Use cmake
+        run: |
+          mkdir builddebug &&
+          cd builddebug &&
+          cmake -DCMAKE_BUILD_TYPE=Debug -DIS_UTF8_CXX_STANDARD=20 ..  &&
+          cmake --build .   &&
+          ctest -j --output-on-failure -LE explicitonly   &&
+          cd .. &&
+          mkdir build &&
+          cd build &&
+          cmake -DIS_UTF8_CXX_STANDARD=20 ..  &&
+          cmake --build .   &&
+          ctest -j --output-on-failure -LE explicitonly

.github/workflows/vs17-cxx20.yml

@@ -0,0 +1,37 @@
+name: VS17-CI (CXX 20)
+
+on: [push, pull_request]
+
+jobs:
+  ci:
+    if: >-
+      ! contains(toJSON(github.event.commits.*.message), '[skip ci]') &&
+      ! contains(toJSON(github.event.commits.*.message), '[skip github]')
+    name: windows-vs17
+    runs-on: windows-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - {gen: Visual Studio 17 2022, arch: x64, shared: ON}
+          - {gen: Visual Studio 17 2022, arch: x64, shared: OFF}
+    steps:
+    - name: checkout
+      uses: actions/checkout@v4
+    - name: Configure
+      run: |
+        cmake -G "${{matrix.gen}}" -A ${{matrix.arch}}
+        -DBUILD_SHARED_LIBS=${{matrix.shared}} -DIS_UTF8_CXX_STANDARD=20
+        -B build
+    - name: Build Debug
+      run: cmake --build build --config Debug --verbose
+    - name: Build Release
+      run: cmake --build build --config Release --verbose
+    - name: Run Release tests
+      run: |
+        cd build
+        ctest -C Release  -LE explicitonly  --output-on-failure
+    - name: Run Debug tests
+      run: |
+        cd build
+        ctest -C Debug  -LE explicitonly  --output-on-failure

CMakeLists.txt

@@ -20,7 +20,11 @@ if (NOT CMAKE_BUILD_TYPE)
   endif()
 endif()
 
-set(CMAKE_CXX_STANDARD 14)
+# We compile tools, tests, etc. with C++ 11. Override yourself if you need on a
+# target.
+set(IS_UTF8_CXX_STANDARD 11 CACHE STRING "the C++ standard to use for is_utf8")
+
+set(CMAKE_CXX_STANDARD ${IS_UTF8_CXX_STANDARD})
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 set(CMAKE_MACOSX_RPATH OFF)
@@ -40,6 +44,8 @@ endif(BUILD_TESTING)
 
 
 add_subdirectory(benchmarks)
+
+message(STATUS "Compiling using the C++ standard:" ${CMAKE_CXX_STANDARD})
 # ---- Install rules ----
 add_library(is_utf8::is_utf8 ALIAS is_utf8)
 

src/is_utf8.cpp

@@ -1116,8 +1116,9 @@ template <typename T, typename Mask = simd8<bool>> struct base_u8 {
     return *this_cast;
   }
 
-  is_utf8_really_inline Mask operator==(const simd8<T> other) const {
-    return vceqq_u8(*this, other);
+  friend is_utf8_really_inline Mask operator==(const simd8<T> lhs,
+                                               const simd8<T> rhs) {
+    return vceqq_u8(lhs, rhs);
   }
 
   template <int N = 1>
@@ -2539,8 +2540,9 @@ struct base8 : base<simd8<T>> {
   is_utf8_really_inline T last() const {
     return _mm256_extract_epi8(*this, 31);
   }
-  is_utf8_really_inline Mask operator==(const simd8<T> other) const {
-    return _mm256_cmpeq_epi8(*this, other);
+  friend is_utf8_really_inline Mask operator==(const simd8<T> lhs,
+                                               const simd8<T> rhs) {
+    return _mm256_cmpeq_epi8(lhs, rhs);
   }
 
   static const int SIZE = sizeof(base<T>::value);
@@ -2965,8 +2967,9 @@ struct base16 : base<simd16<T>> {
   is_utf8_really_inline base16(const Pointer *ptr)
       : base16(_mm256_loadu_si256(reinterpret_cast<const __m256i *>(ptr))) {}
 
-  is_utf8_really_inline Mask operator==(const simd16<T> other) const {
-    return _mm256_cmpeq_epi16(*this, other);
+  friend is_utf8_really_inline Mask operator==(const simd16<T> lhs,
+                                               const simd16<T> rhs) {
+    return _mm256_cmpeq_epi16(lhs, rhs);
   }
 
   /// the size of vector in bytes
@@ -3517,8 +3520,9 @@ struct base8 : base<simd8<T>> {
   is_utf8_really_inline base8() : base<simd8<T>>() {}
   is_utf8_really_inline base8(const __m128i _value) : base<simd8<T>>(_value) {}
 
-  is_utf8_really_inline Mask operator==(const simd8<T> other) const {
-    return _mm_cmpeq_epi8(*this, other);
+  friend is_utf8_really_inline Mask operator==(const simd8<T> lhs,
+                                               const simd8<T> rhs) {
+    return _mm_cmpeq_epi8(lhs, rhs);
   }
 
   static const int SIZE = sizeof(base<simd8<T>>::value);
@@ -4032,8 +4036,9 @@ struct base16 : base<simd16<T>> {
   is_utf8_really_inline base16(const Pointer *ptr)
       : base16(_mm_loadu_si128(reinterpret_cast<const __m128i *>(ptr))) {}
 
-  is_utf8_really_inline Mask operator==(const simd16<T> other) const {
-    return _mm_cmpeq_epi16(*this, other);
+  friend is_utf8_really_inline Mask operator==(const simd16<T> lhs,
+                                               const simd16<T> rhs) {
+    return _mm_cmpeq_epi16(lhs, rhs);
   }
 
   static const int SIZE = sizeof(base<simd16<T>>::value);