diff --git a/src/normal.cc b/src/normal.cc
index 42214a6e..f8097645 100644
--- a/src/normal.cc
+++ b/src/normal.cc
@@ -414,13 +414,10 @@ void replace_with_char(Context& context, NormalParams)
         ScopedEdition edition(context);
         Buffer& buffer = context.buffer();
         SelectionList& selections = context.selections();
-        Vector<String> strings;
-        for (auto& sel : selections)
-        {
-            CharCount count = char_length(buffer, sel);
-            strings.emplace_back(*cp, count);
-        }
-        selections.insert(strings, InsertMode::Replace);
+        selections.insert([&](size_t index, BufferCoord) {
+            CharCount count = char_length(buffer, selections[index]);
+            return String{*cp, count};
+        }, InsertMode::Replace);
     }, "replace with char", "enter char to replace with\n");
 }
 
@@ -438,18 +435,16 @@ void for_each_codepoint(Context& context, NormalParams)
     ScopedEdition edition(context);
     Buffer& buffer = context.buffer();
     SelectionList& selections = context.selections();
-    Vector<String> strings;
-    for (auto& sel : selections)
-    {
+
+    selections.insert([&](size_t index, BufferCoord) {
+        auto& sel = selections[index];
         String str;
         for (auto begin = Utf8It{buffer.iterator_at(sel.min()), buffer},
                   end = Utf8It{buffer.iterator_at(sel.max()), buffer}+1;
              begin != end; ++begin)
             utf8::dump(std::back_inserter(str), func(*begin));
-
-        strings.push_back(std::move(str));
-    }
-    selections.insert(strings, InsertMode::Replace);
+        return str;
+    }, InsertMode::Replace);
 }
 
 void command(const Context& context, EnvVarMap env_vars, char reg = 0)
@@ -649,15 +644,15 @@ void insert_output(Context& context, NormalParams params)
             auto& selections = context.selections();
             const size_t old_main = selections.main_index();
 
-            auto ins = selections | transform([&, i=0](auto& sel) mutable {
-                selections.set_main_index(i++);
-                return ShellManager::instance().eval(
-                    cmdline, context, content(context.buffer(), sel),
-                    ShellManager::Flags::WaitForStdout).first;
-            }) | gather<Vector>();
+            selections.insert([&](size_t index, BufferCoord) {
+                selections.set_main_index(index);
+                auto [out, status] = ShellManager::instance().eval(
+                    cmdline, context, content(context.buffer(), selections[index]),
+                    ShellManager::Flags::WaitForStdout);
+                return out;
+            }, mode);
 
             selections.set_main_index(old_main);
-            selections.insert(ins, mode);
         });
 }
 
@@ -741,7 +736,10 @@ void paste_all(Context& context, NormalParams params)
     auto& selections = context.selections();
     {
         ScopedEdition edition(context);
-        selections.insert(all, effective_mode, &insert_pos);
+        selections.insert([&](size_t, BufferCoord pos) {
+            insert_pos.push_back(pos);
+            return String::no_copy(all);
+        }, effective_mode);
     }
 
     const Buffer& buffer = context.buffer();
diff --git a/src/selection.cc b/src/selection.cc
index 350b3acc..a552526d 100644
--- a/src/selection.cc
+++ b/src/selection.cc
@@ -385,12 +385,18 @@ static void fix_overflowing_selections(Vector<Selection>& selections,
     }
 }
 
-void SelectionList::insert(ConstArrayView<String> strings, InsertMode mode,
-                           Vector<BufferCoord>* out_insert_pos)
+void SelectionList::insert(ConstArrayView<String> strings, InsertMode mode)
 {
     if (strings.empty())
         return;
 
+    insert([&](size_t index, BufferCoord) {
+        return String::no_copy(strings[std::min(strings.size()-1, index)]);
+    }, mode);
+}
+
+void SelectionList::insert(ContentFunc get_content, InsertMode mode)
+{
     update();
 
     Vector<BufferCoord> insert_pos;
@@ -410,11 +416,11 @@ void SelectionList::insert(ConstArrayView<String> strings, InsertMode mode,
         kak_assert(m_buffer->is_valid(sel.anchor()) and
                    m_buffer->is_valid(sel.cursor()));
 
-        const String& str = strings[std::min(index, strings.size()-1)];
-
         const auto pos = (mode == InsertMode::Replace) ?
             sel.min() : changes_tracker.get_new_coord(insert_pos[index]);
 
+        String str = get_content(index, pos);
+
         if (mode == InsertMode::Replace)
         {
             auto range = replace(*m_buffer, sel, str);
@@ -432,8 +438,6 @@ void SelectionList::insert(ConstArrayView<String> strings, InsertMode mode,
         }
 
         changes_tracker.update(*m_buffer, m_timestamp);
-        if (out_insert_pos)
-            out_insert_pos->push_back(pos);
     }
 
     // We might just have been deleting text if strings were empty,
diff --git a/src/selection.hh b/src/selection.hh
index c880aaf7..3c6d879d 100644
--- a/src/selection.hh
+++ b/src/selection.hh
@@ -145,8 +145,9 @@ struct SelectionList
     size_t timestamp() const { return m_timestamp; }
     void force_timestamp(size_t timestamp) { m_timestamp = timestamp; }
 
-    void insert(ConstArrayView<String> strings, InsertMode mode,
-                Vector<BufferCoord>* out_insert_pos = nullptr);
+    void insert(ConstArrayView<String> strings, InsertMode mode);
+    using ContentFunc = FunctionRef<String (size_t index, BufferCoord insert_pos)>;
+    void insert(ContentFunc get_content, InsertMode mode);
     void erase();
 
 private:
diff --git a/src/string.hh b/src/string.hh
index 6fa425e5..d14929f4 100644
--- a/src/string.hh
+++ b/src/string.hh
@@ -124,6 +124,8 @@ public:
     struct NoCopy{};
     String(NoCopy, StringView str);
 
+    static String no_copy(StringView str);
+
     [[gnu::always_inline]]
     char* data() { return m_data.data(); }
 
@@ -274,6 +276,7 @@ template<> struct HashCompatible<StringView, String> : std::true_type {};
 
 inline String::String(StringView str) : String{str.begin(), str.length()} {}
 inline String::String(NoCopy, StringView str) : m_data{NoCopy{}, str.begin(), (size_t)str.length()} {}
+inline String String::no_copy(StringView str) { return {NoCopy{}, str}; }
 
 template<typename Type, typename CharType>
 inline StringView StringOps<Type, CharType>::substr(ByteCount from, ByteCount length) const
diff --git a/src/utils.hh b/src/utils.hh
index 31781907..8dffa9ac 100644
--- a/src/utils.hh
+++ b/src/utils.hh
@@ -173,7 +173,11 @@ public:
         }}
     {}
 
-    template<typename Target, typename = std::enable_if_t<!std::is_same_v<FunctionRef, std::decay_t<Target>>>>
+    template<typename Target,
+             typename = std::enable_if_t<
+                 not std::is_same_v<FunctionRef, std::decay_t<Target>> and
+                 std::is_convertible_v<decltype(std::declval<Target>()(std::declval<Args>()...)), Res>
+             >>
     FunctionRef(Target&& target)
       : m_target{&target},
         m_invoker{[](void* target, Args... args) {