From 88c201167d1d50a1c19480d0f88e28f36c6adcdc Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Fri, 16 Jan 2026 20:47:54 -0500
Subject: [PATCH] xo-expression2: DUniqueSring: fix copy during hypothetical GC

---
 .../include/xo/expression2/DUniqueString.hpp   |  8 +++++++-
 .../src/expression2/DUniqueString.cpp          | 18 ++++++++++++++----
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/xo-expression2/include/xo/expression2/DUniqueString.hpp b/xo-expression2/include/xo/expression2/DUniqueString.hpp
index 46fdfa1e..08fcde86 100644
--- a/xo-expression2/include/xo/expression2/DUniqueString.hpp
+++ b/xo-expression2/include/xo/expression2/DUniqueString.hpp
@@ -59,6 +59,10 @@ namespace xo {
             /** @defgroup duniquestring-methods methods **/
             ///@{
 
+            /** Available storage for this instance.
+             *  For completeness' sake since uniquestring not modifiable
+             **/
+            size_type capacity() const noexcept { return _text()->capacity(); }
             size_type size() const noexcept { return _text()->size(); }
             const char * chars() const noexcept { return _text()->chars(); }
 
@@ -74,6 +78,8 @@ namespace xo {
 
             std::size_t hash() const noexcept { return _text()->hash(); }
             operator std::string_view() const noexcept { return std::string_view(*_text()); }
+            /** not assignable **/
+            DUniqueString & operator=(const DUniqueString &) = delete;
 
             ///@}
             /** @defgroup duniquestring-printable-methods printable facet methods **/
@@ -105,7 +111,7 @@ namespace xo {
             /** DString containing actual string content immediately follows DUniqueString
              *  in memory; part of same alloc
              **/
-            const DString * _text() const noexcept;
+            DString * _text() const noexcept;
 
             //explicit DUniqueString(const DString * text) : text_{text} {}
 
diff --git a/xo-expression2/src/expression2/DUniqueString.cpp b/xo-expression2/src/expression2/DUniqueString.cpp
index d0a4b0a0..c0fa26db 100644
--- a/xo-expression2/src/expression2/DUniqueString.cpp
+++ b/xo-expression2/src/expression2/DUniqueString.cpp
@@ -6,13 +6,14 @@
 #include "DUniqueString.hpp"
 #include <xo/arena/padding.hpp>
 #include <xo/indentlog/scope.hpp>
+#include <cstring>
 
 namespace xo {
     using xo::mm::padding;
     using xo::facet::typeseq;
 
     namespace scm {
-        const DString *
+        DString *
         DUniqueString::_text() const noexcept
         {
             // location of paired DString is chosen
@@ -30,7 +31,7 @@ namespace xo {
             size_t offset = padding::with_padding(sizeof(*this));
             assert(offset > 0);
 
-            return (const DString *)(((std::byte *)this) + offset);
+            return (DString *)(((std::byte *)this) + offset);
         }
 
         bool
@@ -84,8 +85,17 @@ namespace xo {
 
             DUniqueString * copy = (DUniqueString *)mm.alloc_copy((std::byte *)this);
 
-            if (copy)
-                *copy = *this;
+            if (copy) {
+                // Copy assignment not implemented in general
+                //   *copy = *this;
+                // in this case *copy already has the same size as *this
+
+                assert(size() <= capacity());
+
+                strncpy(copy->_text()->data(),
+                        this->_text()->chars(),
+                        this->size());
+            }
 
             return copy;
         }