Replace string concatenation with StringBuilder and invariant interpolation

QRCoder/Attributes/InterpolatedStringHandlerAttributes.cs

@@ -0,0 +1,80 @@
+#if !NET6_0_OR_GREATER
+namespace System.Runtime.CompilerServices;
+
+/// <summary>
+/// Indicates the attributed type is an interpolated string handler.
+/// </summary>
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, Inherited = false)]
+internal sealed class InterpolatedStringHandlerAttribute : Attribute
+{
+}
+
+/// <summary>
+/// Indicates which arguments an interpolated string handler passes through to the underlying handler constructor.
+/// </summary>
+[AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
+internal sealed class InterpolatedStringHandlerArgumentAttribute : Attribute
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="InterpolatedStringHandlerArgumentAttribute"/> class.
+    /// </summary>
+    /// <param name="argument">The name of the argument that should be passed to the handler.</param>
+    public InterpolatedStringHandlerArgumentAttribute(string argument)
+    {
+        Arguments = new[] { argument };
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="InterpolatedStringHandlerArgumentAttribute"/> class.
+    /// </summary>
+    /// <param name="argument1">The name of the first argument that should be passed to the handler.</param>
+    /// <param name="argument2">The name of the second argument that should be passed to the handler.</param>
+    public InterpolatedStringHandlerArgumentAttribute(string argument1, string argument2)
+    {
+        Arguments = new[] { argument1, argument2 };
+    }
+
+    /// <summary>
+    /// Gets the arguments that should be passed to the handler.
+    /// </summary>
+    public string[] Arguments { get; }
+}
+
+/// <summary>
+/// Indicates that compiler support for a particular feature is required for the location where this attribute is applied.
+/// </summary>
+[AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]
+internal sealed class CompilerFeatureRequiredAttribute : Attribute
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="CompilerFeatureRequiredAttribute"/> class.
+    /// </summary>
+    /// <param name="featureName">The name of the compiler feature.</param>
+    public CompilerFeatureRequiredAttribute(string featureName)
+    {
+        FeatureName = featureName;
+    }
+
+    /// <summary>
+    /// Gets the name of the compiler feature.
+    /// </summary>
+    public string FeatureName { get; }
+
+    /// <summary>
+    /// Gets a value that indicates whether the compiler can choose to allow access if it does not understand <see cref="FeatureName"/>.
+    /// </summary>
+    public bool IsOptional { get; set; }
+
+    /// <summary>
+    /// The feature name used for ref structs.
+    /// </summary>
+#pragma warning disable IDE1006 // Must match the BCL constant names
+    public const string RefStructs = nameof(RefStructs);
+
+    /// <summary>
+    /// The feature name used for required members.
+    /// </summary>
+    public const string RequiredMembers = nameof(RequiredMembers);
+#pragma warning restore IDE1006
+}
+#endif

QRCoder/Extensions/StringExtensions.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
 
 namespace QRCoder;
 
@@ -67,6 +68,21 @@ internal static string ToString(this char c, CultureInfo _)
         => c.ToString();
 #endif
 
+    /// <summary>
+    /// Appends an interpolated string using invariant culture formatting.
+    /// On .NET 6+ appends via the invariant-culture interpolated-string handler overload (no extra string allocation).
+    /// Must be a static method (not an extension) so the handler can reference the <paramref name="sb"/> parameter (CS8944).
+    /// </summary>
+#if NET6_0_OR_GREATER
+    internal static void AppendInvariant(
+        StringBuilder sb,
+        [InterpolatedStringHandlerArgument(nameof(sb))] ref StringBuilder.AppendInterpolatedStringHandler handler)
+        => sb.Append(CultureInfo.InvariantCulture, ref handler);
+#else
+    internal static void AppendInvariant(StringBuilder sb, string value)
+        => sb.Append(value);
+#endif
+
     /// <summary>
     /// Appends an integer value to the StringBuilder using invariant culture formatting.
     /// </summary>
@@ -75,7 +91,7 @@ internal static string ToString(this char c, CultureInfo _)
     internal static void AppendInvariant(this StringBuilder sb, int num)
     {
 #if NET6_0_OR_GREATER
-        sb.Append(CultureInfo.InvariantCulture, $"{num}");
+        AppendInvariant(sb, $"{num}");
 #else
 #if HAS_SPAN
         Span<char> buffer = stackalloc char[16];
@@ -97,7 +113,7 @@ internal static void AppendInvariant(this StringBuilder sb, int num)
     internal static void AppendInvariant(this StringBuilder sb, float num)
     {
 #if NET6_0_OR_GREATER
-        sb.Append(CultureInfo.InvariantCulture, $"{num:G7}");
+        AppendInvariant(sb, $"{num:G7}");
 #else
 #if HAS_SPAN
         Span<char> buffer = stackalloc char[16];

QRCoder/PayloadGenerator.cs

@@ -24,7 +24,16 @@ internal static bool IsValidIban(string iban)
 
         //Check IBAN checksum
         var checksumValid = false;
-        var sum = $"{ibanCleared.Substring(4)}{ibanCleared.Substring(0, 4)}".ToCharArray().Aggregate("", (current, c) => current + (char.IsLetter(c) ? (c - 55).ToString(CultureInfo.InvariantCulture) : c.ToString(CultureInfo.InvariantCulture)));
+        var sumChars = $"{ibanCleared.Substring(4)}{ibanCleared.Substring(0, 4)}".ToCharArray();
+        var sumBuilder = new StringBuilder(sumChars.Length * 2);
+        foreach (var c in sumChars)
+        {
+            if (char.IsLetter(c))
+                sumBuilder.Append((c - 55).ToString(CultureInfo.InvariantCulture));
+            else
+                sumBuilder.Append(c);
+        }
+        var sum = sumBuilder.ToString();
         int m = 0;
         for (int i = 0; i < (int)Math.Ceiling((sum.Length - 2) / 7d); i++)
         {
@@ -33,7 +42,7 @@ internal static bool IsValidIban(string iban)
 #if NET5_0_OR_GREATER
             var n = string.Concat(i == 0 ? "" : m.ToString(CultureInfo.InvariantCulture), sum.AsSpan(start, Math.Min(9 - offset, sum.Length - start)));
 #else
-            var n = (i == 0 ? "" : m.ToString(CultureInfo.InvariantCulture)) + sum.Substring(start, Math.Min(9 - offset, sum.Length - start));
+            var n = $"{(i == 0 ? "" : m.ToString(CultureInfo.InvariantCulture))}{sum.Substring(start, Math.Min(9 - offset, sum.Length - start))}";
 #endif
             if (!int.TryParse(n, NumberStyles.Any, CultureInfo.InvariantCulture, out m))
                 break;
@@ -112,7 +121,7 @@ private static string EscapeInput(string inp, bool simple = false)
         }
         foreach (var c in forbiddenChars)
         {
-            inp = inp.Replace(c.ToString(), "\\" + c);
+            inp = inp.Replace(c.ToString(), $"\\{c}");
         }
         return inp;
     }

QRCoder/PayloadGenerator/BezahlCode.cs

@@ -148,7 +148,7 @@
             _name = name;
 
             //Limit reason length depending on payment type
-            //140 chars for SEPA payments and 27 chars for others 
+            //140 chars for SEPA payments and 27 chars for others
             var reasonLength = authority == AuthorityType.periodicsinglepaymentsepa || authority == AuthorityType.singledirectdebitsepa || authority == AuthorityType.singlepaymentsepa || (authority == AuthorityType.contact_v2 && newWayFilled) ? 140 : 27;
             if (reason.Length > reasonLength)
                 throw new BezahlCodeException($"Reasons texts have to be shorter than {reasonLength + 1} chars.");
@@ -246,9 +246,8 @@
         /// <inheritdoc/>
         public override string ToString()
         {
-            var bezahlCodePayload = $"bank://{_authority}?";
-
-            bezahlCodePayload += $"name={Uri.EscapeDataString(_name)}&";
+            var bezahlCodePayload = new StringBuilder($"bank://{_authority}?");
+            StringExtensions.AppendInvariant(bezahlCodePayload,$"name={Uri.EscapeDataString(_name)}&");
 
             if (_authority != AuthorityType.contact && _authority != AuthorityType.contact_v2)
             {
@@ -257,44 +256,44 @@
                 if (_authority == AuthorityType.periodicsinglepayment || _authority == AuthorityType.singledirectdebit || _authority == AuthorityType.singlepayment)
 #pragma warning restore CS0618
                 {
-                    bezahlCodePayload += $"account={_account}&";
-                    bezahlCodePayload += $"bnc={_bnc}&";
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"account={_account}&");
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"bnc={_bnc}&");
                     if (_postingKey > 0)
-                        bezahlCodePayload += $"postingkey={_postingKey}&";
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"postingkey={_postingKey}&");
                 }
                 else
                 {
-                    bezahlCodePayload += $"iban={_iban}&";
-                    bezahlCodePayload += $"bic={_bic}&";
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"iban={_iban}&");
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"bic={_bic}&");
 
                     if (!string.IsNullOrEmpty(_sepaReference))
-                        bezahlCodePayload += $"separeference={Uri.EscapeDataString(_sepaReference)}&";
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"separeference={Uri.EscapeDataString(_sepaReference)}&");
 
                     if (_authority == AuthorityType.singledirectdebitsepa)
                     {
                         if (!string.IsNullOrEmpty(_creditorId))
-                            bezahlCodePayload += $"creditorid={Uri.EscapeDataString(_creditorId)}&";
+                            StringExtensions.AppendInvariant(bezahlCodePayload,$"creditorid={Uri.EscapeDataString(_creditorId)}&");
                         if (!string.IsNullOrEmpty(_mandateId))
-                            bezahlCodePayload += $"mandateid={Uri.EscapeDataString(_mandateId)}&";
+                            StringExtensions.AppendInvariant(bezahlCodePayload,$"mandateid={Uri.EscapeDataString(_mandateId)}&");
                         if (_dateOfSignature != DateTime.MinValue)
-                            bezahlCodePayload += $"dateofsignature={_dateOfSignature.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&";
+                            StringExtensions.AppendInvariant(bezahlCodePayload,$"dateofsignature={_dateOfSignature.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&");
                     }
                 }
-                bezahlCodePayload += string.Format(CultureInfo.InvariantCulture, "amount={0:0.00}&", _amount).Replace(".", ",");
+                bezahlCodePayload.Append(string.Format(CultureInfo.InvariantCulture, "amount={0:0.00}&", _amount).Replace(".", ","));
 
                 if (!string.IsNullOrEmpty(_reason))
-                    bezahlCodePayload += $"reason={Uri.EscapeDataString(_reason)}&";
-                bezahlCodePayload += $"currency={_currency}&";
-                bezahlCodePayload += $"executiondate={_executionDate.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&";
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"reason={Uri.EscapeDataString(_reason)}&");
+                StringExtensions.AppendInvariant(bezahlCodePayload,$"currency={_currency}&");
+                StringExtensions.AppendInvariant(bezahlCodePayload,$"executiondate={_executionDate.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&");
 #pragma warning disable CS0618
                 if (_authority == AuthorityType.periodicsinglepayment || _authority == AuthorityType.periodicsinglepaymentsepa)
                 {
-                    bezahlCodePayload += $"periodictimeunit={_periodicTimeunit}&";
-                    bezahlCodePayload += $"periodictimeunitrotation={_periodicTimeunitRotation}&";
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"periodictimeunit={_periodicTimeunit}&");
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"periodictimeunitrotation={_periodicTimeunitRotation}&");
                     if (_periodicFirstExecutionDate != DateTime.MinValue)
-                        bezahlCodePayload += $"periodicfirstexecutiondate={_periodicFirstExecutionDate.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&";
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"periodicfirstexecutiondate={_periodicFirstExecutionDate.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&");
                     if (_periodicLastExecutionDate != DateTime.MinValue)
-                        bezahlCodePayload += $"periodiclastexecutiondate={_periodicLastExecutionDate.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&";
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"periodiclastexecutiondate={_periodicLastExecutionDate.ToString("ddMMyyyy", CultureInfo.InvariantCulture)}&");
                 }
 #pragma warning restore CS0618
             }
@@ -303,28 +302,29 @@
                 //Handle what is same for all contacts
                 if (_authority == AuthorityType.contact)
                 {
-                    bezahlCodePayload += $"account={_account}&";
-                    bezahlCodePayload += $"bnc={_bnc}&";
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"account={_account}&");
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"bnc={_bnc}&");
                 }
                 else if (_authority == AuthorityType.contact_v2)
                 {
                     if (!string.IsNullOrEmpty(_account) && !string.IsNullOrEmpty(_bnc))
                     {
-                        bezahlCodePayload += $"account={_account}&";
-                        bezahlCodePayload += $"bnc={_bnc}&";
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"account={_account}&");
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"bnc={_bnc}&");
                     }
                     else
                     {
-                        bezahlCodePayload += $"iban={_iban}&";
-                        bezahlCodePayload += $"bic={_bic}&";
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"iban={_iban}&");
+                        StringExtensions.AppendInvariant(bezahlCodePayload,$"bic={_bic}&");
                     }
                 }
 
                 if (!string.IsNullOrEmpty(_reason))
-                    bezahlCodePayload += $"reason={Uri.EscapeDataString(_reason)}&";
+                    StringExtensions.AppendInvariant(bezahlCodePayload,$"reason={Uri.EscapeDataString(_reason)}&");
             }
 
-            return bezahlCodePayload.Trim('&');
+            string result = bezahlCodePayload.ToString();
+            return result.TrimEnd('&');
         }
 
         /// <summary>

QRCoder/PayloadGenerator/BitcoinLikeCryptoCurrencyAddress.cs

@@ -55,10 +55,10 @@ public override string ToString()
 
             if (queryValues.Any(keyPair => !string.IsNullOrEmpty(keyPair.Value)))
             {
-                query = "?" + string.Join("&", queryValues
+                query = $"?{string.Join("&", queryValues
                     .Where(keyPair => !string.IsNullOrEmpty(keyPair.Value))
                     .Select(keyPair => $"{keyPair.Key}={keyPair.Value}")
-                    .ToArray());
+                    .ToArray())}";
             }
 
             return $"{Enum.GetName(typeof(BitcoinLikeCryptoCurrencyType), _currencyType)!.ToLowerInvariant()}:{_address}{query}";