introduce OUStringConstExpr

so we can declare compile-time constant arrays and structs
containing OUStringLiteral

Change-Id: I51fd743f2e461a36bb4a0a17c6ff107f86096895
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/125045
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

1 files changed, 35 insertions, 0 deletions

diff --git a/include/rtl/ustring.hxx b/include/rtl/ustring.hxx
index 1a5ff2d97d6c..6cf92e1d3599 100644
--- a/include/rtl/ustring.hxx
+++ b/include/rtl/ustring.hxx
@@ -84,6 +84,7 @@ template<std::size_t N> class SAL_WARN_UNUSED OUStringLiteral {
     static_assert(N != 0);
     static_assert(N - 1 <= std::numeric_limits<sal_Int32>::max(), "literal too long");
     friend class OUString;
+    friend class OUStringConstExpr;
 
 public:
 #if HAVE_CPP_CONSTEVAL
@@ -138,6 +139,34 @@ template<std::size_t N> struct ExceptCharArrayDetector<OUStringLiteral<N>> {};
 }
 #endif
 
+/**
+  This is intended to be used when declaring compile-time-constant structs or arrays
+  that can be initialised from named OUStringLiteral e.g.
+
+    constexpr OUStringLiteral AAA = u"aaa";
+    constexpr OUStringLiteral BBB = u"bbb";
+    constexpr OUStringConstExpr FOO[] { AAA, BBB };
+*/
+class OUString;
+class OUStringConstExpr
+{
+public:
+    template<std::size_t N> constexpr OUStringConstExpr(OUStringLiteral<N> const & literal):
+        pData(const_cast<rtl_uString *>(&literal.str)) {}
+    
+    // prevent mis-use
+    template<std::size_t N> constexpr OUStringConstExpr(OUStringLiteral<N> && literal)
+        = delete;
+
+    // no destructor necessary because we know we are pointing at a compile-time
+    // constant OUStringLiteral, which bypasses ref-counting.
+
+    inline operator OUString() const;
+
+private:
+    rtl_uString* pData;
+};
+
 /// @endcond
 #endif
 
@@ -3269,6 +3298,11 @@ private:
 };
 
 #if defined LIBO_INTERNAL_ONLY
+// Can only define this after we define OUString
+inline OUStringConstExpr::operator OUString() const { return OUString::unacquired(&pData); }
+#endif
+
+#if defined LIBO_INTERNAL_ONLY
 // Prevent the operator ==/!= overloads with 'sal_Unicode const *' parameter from
 // being selected for nonsensical code like
 //
@@ -3328,6 +3362,7 @@ inline std::basic_ostream<charT, traits> & operator <<(
     return stream << OUString( std::move(concat) );
 }
 
+    
 /// @endcond
 #endif