From 4c468d88e34e92e3100de9071f8aaf7e7d0b9c35 Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Tue, 13 Jan 2026 17:07:03 -0500
Subject: [PATCH] xo-object2: + DString::assign

---
 xo-object2/include/xo/object2/DString.hpp | 63 +++++++++++++++++++++++
 xo-object2/src/object2/DString.cpp        | 13 +++++
 xo-object2/utest/DString.test.cpp         | 32 ++++++++++++
 3 files changed, 108 insertions(+)

diff --git a/xo-object2/include/xo/object2/DString.hpp b/xo-object2/include/xo/object2/DString.hpp
index 6333f7a4..dbd72ddf 100644
--- a/xo-object2/include/xo/object2/DString.hpp
+++ b/xo-object2/include/xo/object2/DString.hpp
@@ -7,6 +7,7 @@
 
 #include <xo/alloc2/Allocator.hpp>
 #include <xo/facet/obj.hpp>
+#include <string_view>
 #include <cstdint>
 
 namespace xo {
@@ -27,6 +28,9 @@ namespace xo {
             using size_type = std::uint32_t;
             using AAllocator = xo::mm::AAllocator;
 
+            /** @defgroup dstring-ctors constructors **/
+            ///@{
+
             /** create empty string with space for @cap chars
              *  (including null terminator).
              *  Use memory from allocator @p mm
@@ -40,10 +44,69 @@ namespace xo {
             static DString * from_cstr(obj<AAllocator> mm,
                                        const char * cstr);
 
+            ///@}
+            /** @defgroup dstring-access access methods **/
+            ///@{
+
             size_type capacity() const noexcept { return capacity_; }
             size_type size() const noexcept { return size_; }
             const char * chars() const noexcept { return chars_; }
 
+            ///@}
+            /** @defgroup dstring-iterators iterators **/
+            ///@{
+
+            ///@}
+            /** @defgroup dstring-assign assignment **/
+            ///@{
+
+            /** put string into empty state **/
+            void clear() noexcept { size_ = 0; chars_[0] = '\0'; }
+
+            /** replace contents with @p other, or prefix of up to @p capacity - 1 chars **/
+            DString & assign(const DString & other);
+
+            // TODO - behave like std::string, to the extent feasible
+            //   insert
+            //   insert_range
+            //   erase
+            //   push_back
+            //   append
+            //   append_range
+            //   operator+=
+            // replace
+            // replace_with_range
+            // copy
+            // find
+            // rfind
+            // find_first_of
+            // find_first_not_of
+            // find_last_of
+            // find_last_not_of
+            // compare
+            // starts_with
+            // end_with
+            // contains
+            // substr
+
+            ///@}
+            /** @defgroup dstring-conversion-operators conversion operators **/
+            ///@{
+
+            operator std::string_view() const noexcept { return std::string_view(chars_); }
+
+            /** @brief conversion oeprator to C-style string.
+             *
+             *  Example
+             *  @code
+             *    DString s = ...;
+             *    ::strcmp(s, "obey...");
+             *  @endcode
+             **/
+            operator const char * () const noexcept { return &(chars_[0]); }
+
+            ///@}
+
         private:
             /** extent of @ref chars_ array **/
             size_type capacity_ = 0;
diff --git a/xo-object2/src/object2/DString.cpp b/xo-object2/src/object2/DString.cpp
index 7f5aee15..53feef8c 100644
--- a/xo-object2/src/object2/DString.cpp
+++ b/xo-object2/src/object2/DString.cpp
@@ -4,6 +4,7 @@
  **/
 
 #include "DString.hpp"
+#include <algorithm>
 #include <cstring>
 
 namespace xo {
@@ -50,6 +51,18 @@ namespace xo {
 
             return result;
         }
+
+        DString &
+        DString::assign(const DString & other)
+        {
+            size_type n = std::min(other.size_, capacity_ - 1);
+            std::memcpy(chars_, other.chars_, n);
+            chars_[n] = '\0';
+            size_ = n;
+
+            return *this;
+        }
+
     } /*namespace scm*/
 } /*namespace xo*/
 
diff --git a/xo-object2/utest/DString.test.cpp b/xo-object2/utest/DString.test.cpp
index c3437b6b..0bc3e596 100644
--- a/xo-object2/utest/DString.test.cpp
+++ b/xo-object2/utest/DString.test.cpp
@@ -47,6 +47,38 @@ namespace xo {
             REQUIRE(s->size() == 11);
             REQUIRE(std::strcmp(s->chars(), cstr) == 0);
         }
+
+        TEST_CASE("DString-assign", "[object2][DString]")
+        {
+            ArenaConfig cfg { .name_ = "testarena",
+                              .size_ = 4*1024 };
+            DArena arena = DArena::map(cfg);
+            auto alloc = with_facet<AAllocator>::mkobj(&arena);
+
+            DString * src = DString::from_cstr(alloc, "hello");
+            DString * dst = DString::empty(alloc, 16);
+
+            dst->assign(*src);
+
+            REQUIRE(dst->size() == 5);
+            REQUIRE(std::strcmp(dst->chars(), "hello") == 0);
+        }
+
+        TEST_CASE("DString-assign-truncate", "[object2][DString]")
+        {
+            ArenaConfig cfg { .name_ = "testarena",
+                              .size_ = 4*1024 };
+            DArena arena = DArena::map(cfg);
+            auto alloc = with_facet<AAllocator>::mkobj(&arena);
+
+            DString * src = DString::from_cstr(alloc, "hello world");
+            DString * dst = DString::empty(alloc, 6);
+
+            dst->assign(*src);
+
+            REQUIRE(dst->size() == 5);
+            REQUIRE(std::strcmp(dst->chars(), "hello") == 0);
+        }
     } /*namespace ut*/
 } /*namespace xo*/