Use span-based string.Concat to avoid unnecessary allocation

Calling Substring produces a copy of the extracted substring. By using AsSpan instead of Substring and calling the overload of string.Concat that accepts spans, you can eliminate the unnecessary string allocation.

.editorconfig

@@ -194,7 +194,6 @@ dotnet_diagnostic.CA1819.severity = suggestion
 dotnet_diagnostic.CA1822.severity = suggestion
 dotnet_diagnostic.CA1823.severity = suggestion
 dotnet_diagnostic.CA1824.severity = suggestion
-dotnet_diagnostic.CA1845.severity = suggestion
 dotnet_diagnostic.CA1846.severity = suggestion
 dotnet_diagnostic.CA1847.severity = suggestion
 dotnet_diagnostic.CA2000.severity = suggestion

src/NzbDrone.Common/Http/HttpUri.cs

@@ -170,7 +170,7 @@ namespace NzbDrone.Common.Http
 
             if (baseSlashIndex >= 0)
             {
-                return basePath.Substring(0, baseSlashIndex) + "/" + relativePath;
+                return $"{basePath.AsSpan(0, baseSlashIndex)}/{relativePath}";
             }
 
             return relativePath;

src/NzbDrone.Core/Notifications/Discord/Discord.cs

@@ -69,7 +69,7 @@ namespace NzbDrone.Core.Notifications.Discord
                     case DiscordGrabFieldType.Overview:
                         var overview = episodes.First().Overview ?? "";
                         discordField.Name = "Overview";
-                        discordField.Value = overview.Length <= 300 ? overview : overview.Substring(0, 300) + "...";
+                        discordField.Value = overview.Length <= 300 ? overview : $"{overview.AsSpan(0, 300)}...";
                         break;
                     case DiscordGrabFieldType.Rating:
                         discordField.Name = "Rating";
@@ -160,7 +160,7 @@ namespace NzbDrone.Core.Notifications.Discord
                     case DiscordImportFieldType.Overview:
                         var overview = episodes.First().Overview ?? "";
                         discordField.Name = "Overview";
-                        discordField.Value = overview.Length <= 300 ? overview : overview.Substring(0, 300) + "...";
+                        discordField.Value = overview.Length <= 300 ? overview : $"{overview.AsSpan(0, 300)}...";
                         break;
                     case DiscordImportFieldType.Rating:
                         discordField.Name = "Rating";

src/NzbDrone.Core/Parser/Parser.cs

@@ -545,7 +545,7 @@ namespace NzbDrone.Core.Parser
                 var titleWithoutExtension = RemoveFileExtension(title).ToCharArray();
                 Array.Reverse(titleWithoutExtension);
 
-                title = new string(titleWithoutExtension) + title.Substring(titleWithoutExtension.Length);
+                title = string.Concat(new string(titleWithoutExtension), title.AsSpan(titleWithoutExtension.Length));
 
                 Logger.Debug("Reversed name detected. Converted to '{0}'", title);
             }
@@ -576,7 +576,7 @@ namespace NzbDrone.Core.Parser
                     var titleWithoutExtension = RemoveFileExtension(title).ToCharArray();
                     Array.Reverse(titleWithoutExtension);
 
-                    title = new string(titleWithoutExtension) + title.Substring(titleWithoutExtension.Length);
+                    title = string.Concat(new string(titleWithoutExtension), title.AsSpan(titleWithoutExtension.Length));
 
                     Logger.Debug("Reversed name detected. Converted to '{0}'", title);
                 }