less copies and allocations in replaceInPlace

1 files changed, 20 insertions, 7 deletions

diff --git a/src/catch2/internal/catch_string_manip.cpp b/src/catch2/internal/catch_string_manip.cpp
index 0c889ca1..ce1abaa0 100644
--- a/src/catch2/internal/catch_string_manip.cpp
+++ b/src/catch2/internal/catch_string_manip.cpp
@@ -5,6 +5,7 @@
 //        https://www.boost.org/LICENSE_1_0.txt)
 
 // SPDX-License-Identifier: BSL-1.0
+#include <catch2/internal/catch_move_and_forward.hpp>
 #include <catch2/internal/catch_string_manip.hpp>
 #include <catch2/internal/catch_stringref.hpp>
 
@@ -65,17 +66,29 @@ namespace Catch {
     }
 
     bool replaceInPlace( std::string& str, std::string const& replaceThis, std::string const& withThis ) {
-        bool replaced = false;
         std::size_t i = str.find( replaceThis );
-        while( i != std::string::npos ) {
-            replaced = true;
-            str = str.substr( 0, i ) + withThis + str.substr( i+replaceThis.size() );
-            if( i < str.size()-withThis.size() )
-                i = str.find( replaceThis, i+withThis.size() );
+        if (i == std::string::npos) {
+            return false;
+        }
+        std::size_t copyBegin = 0;
+        std::string origStr = CATCH_MOVE(str);
+        str.clear();
+        // There is at least one replacement, so reserve with the best guess
+        // we can make without actually counting the number of occurences.
+        str.reserve(origStr.size() - replaceThis.size() + withThis.size());
+        do {
+            str.append(origStr, copyBegin, i-copyBegin );
+            str += withThis;
+            copyBegin = i + replaceThis.size();
+            if( copyBegin < origStr.size() )
+                i = origStr.find( replaceThis, copyBegin );
             else
                 i = std::string::npos;
+        } while( i != std::string::npos );
+        if ( copyBegin < origStr.size() ) {
+            str.append(origStr, copyBegin, origStr.size() );
         }
-        return replaced;
+        return true;
     }
 
     std::vector<StringRef> splitStringRef( StringRef str, char delimiter ) {