dotnet · rolfbjarne · May 27, 2026 · May 25, 2026 · May 25, 2026 · May 25, 2026
diff --git a/docs/website/binding_types_reference_guide.md b/docs/website/binding_types_reference_guide.md
@@ -1306,28 +1306,9 @@ This should map to Objective-C/clang use of `__attribute__((objc_designated_init
 
 ### DisableZeroCopyAttribute
 
-This attribute is applied to string parameters or string properties and
-instructs the code generator to not use the zero-copy string marshaling for
-this parameter, and instead create a new NSString instance from the C# string.
-This attribute is only required on strings if you instruct the generator to use
-zero-copy string marshaling using either the `--zero-copy` command
-line option or setting the assembly-level attribute `ZeroCopyStringsAttribute`.
-
-This is necessary in cases where the property is declared in Objective-C to
-be a `retain` or `assign` property instead of a `copy` property. These typically
-happen in third-party libraries that have been wrongly "optimized" by
-developers. In general, `retain` or `assign` `NSString` properties are incorrect
-since `NSMutableString` or user-derived classes of `NSString` might alter the
-contents of the strings without the knowledge of the library code, subtly
-breaking the application. Typically this happens due to premature
-optimization.
-
-The following shows two such properties in Objective-C:
-
-```csharp
-@property(nonatomic,retain) NSString *name;
-@property(nonatomic,assign) NSString *name2;
-```
+> **Note:** This attribute is obsolete and has no effect. Zero-copy string
+> marshaling is no longer supported. The attribute is preserved for source
+> compatibility but can be safely removed from binding definitions.
 
 <a name="DisposeAttribute"></a>
 
@@ -2435,47 +2416,10 @@ This corresponds to `clang` [`__attribute__((objc_requires_super))`](https://cla
 
 ### ZeroCopyStringsAttribute
 
-Only available in Xamarin.iOS 5.4 and newer.
-
-This attribute instructs the generator that the binding for this specific
-library (if applied with `[assembly:]`) or type should use the fast
-zero-copy string marshaling. This attribute is equivalent to passing the
-command line option `--zero-copy` to the generator.
-
-When using zero-copy for strings, the generator effectively uses the same C#
-string as the string that Objective-C consumes without incurring the creation of
-a new `NSString` object and avoiding copying the data from the C# strings to the
-Objective-C string. The only drawback of using Zero Copy strings is that you
-must ensure that any string property that you wrap that happens to be flagged as
-`retain` or `copy` has the `[DisableZeroCopy]` attribute set. This is
-require because the handle for zero-copy strings is allocated on the stack and
-is invalid upon the function return.
-
-Example:
-
-```csharp
-[ZeroCopyStrings]
-[BaseType (typeof (NSObject))]
-interface MyBinding {
-    [Export ("name")]
-    string Name { get; set; }
-
-    [Export ("domain"), NullAllowed]
-    string Domain { get; set; }
-
-    [DisablZeroCopy]
-    [Export ("someRetainedNSString")]
-    string RetainedProperty { get; set; }
-}
-
-```
-
-You can also apply the attribute at the assembly level, and it will apply to
-all the types of the assembly:
-
-```csharp
-[assembly:ZeroCopyStrings]
-```
+> **Note:** This attribute is obsolete and has no effect. Zero-copy string
+> marshaling is no longer supported. The `--use-zero-copy` command line option
+> is also no longer supported. The attribute is preserved for source
+> compatibility but can be safely removed from binding definitions.
 
 ## Strongly-typed dictionaries
 

diff --git a/docs/website/generator-errors.md b/docs/website/generator-errors.md
@@ -128,7 +128,7 @@ Please go to [[FieldAttribute]](https://developer.xamarin.com/guides/cross-platf
 
 ### <a name='BI1026'/>BI1026: `*`: Enums attributed with [\*] must have an underlying type of `long` or `ulong`
 
-### <a name='BI1027'/>BI1027: Support for ZeroCopy strings is not implemented. Strings will be marshalled as NSStrings.
+### <a name='BI1027'/>BI1027: Support for ZeroCopy strings is not implemented. The --use-zero-copy option is not supported and will be ignored.
 
 ### <a name='BI1028'/>BI1028: Internal sanity check failed, please file a bug report (https://github.com/dotnet/macios/issues/new) with a test case.
 

diff --git a/src/ObjCBindings/ExportTag.cs b/src/ObjCBindings/ExportTag.cs
@@ -1,3 +1,4 @@
+using System.ComponentModel;
 using System.Diagnostics.CodeAnalysis;
 
 #nullable enable
@@ -169,18 +170,10 @@ public enum Property : Int64 {
 		CustomMarshalDirective = 1 << 5,
 
 		/// <summary>
-		/// Apply to strings parameters that are merely retained or assigned,
-		/// not copied this is an exception as it is advised in the coding
-		/// standard for Objective-C to avoid this, but a few properties do use
-		/// this.  Use this falg for properties flagged with `retain' or
-		/// `assign', which look like this:
-		///
-		/// @property (retain) NSString foo;
-		/// @property (assign) NSString assigned;
-		///
-		/// This forced the generator to create an NSString before calling the
-		/// API instead of using the fast string marshalling code.
+		/// This flag is obsolete and has no effect. Zero-copy string marshaling is no longer supported.
 		/// </summary>
+		[EditorBrowsable (EditorBrowsableState.Never)]
+		[Obsolete ("Zero-copy string marshaling is no longer supported. This flag has no effect.")]
 		DisableZeroCopy = 1 << 6,
 
 		/// <summary>

diff --git a/src/Resources.Designer.cs b/src/Resources.Designer.cs
diff --git a/src/Resources.resx b/src/Resources.resx
@@ -294,7 +294,7 @@
 	</data>
 
 	<data name="BI1027" xml:space="preserve">
-		<value>Support for ZeroCopy strings is not implemented. Strings will be marshalled as NSStrings.</value>
+		<value>The --use-zero-copy option is not supported and will be ignored.</value>
 	</data>
 
 	<data name="BI1028" xml:space="preserve">

diff --git a/src/bgen/Attributes.cs b/src/bgen/Attributes.cs
@@ -517,20 +517,14 @@ public class NoDefaultValueAttribute : Attribute {
 public class IgnoredInDelegateAttribute : Attribute {
 }
 
-// Apply to strings parameters that are merely retained or assigned,
-// not copied this is an exception as it is advised in the coding
-// standard for Objective-C to avoid this, but a few properties do use
-// this.  Use this attribtue for properties flagged with `retain' or
-// `assign', which look like this:
-//
-// @property (retain) NSString foo;
-// @property (assign) NSString assigned;
-//
-// This forced the generator to create an NSString before calling the
-// API instead of using the fast string marshalling code.
+#if !XAMCORE_5_0
+// This attribute is obsolete and has no effect. Zero-copy string marshaling is no longer supported.
+[Obsolete ("Zero-copy string marshaling is no longer supported. This attribute has no effect.")]
+[AttributeUsage (AttributeTargets.Property | AttributeTargets.Parameter, AllowMultiple = true)]
 public class DisableZeroCopyAttribute : Attribute {
 	public DisableZeroCopyAttribute () { }
 }
+#endif
 
 // Apply this attribute to methods that need a custom binding method.
 //
@@ -561,29 +555,13 @@ public class MarshalDirectiveAttribute : Attribute {
 	public string? Library { get; set; }
 }
 
-//
-// By default, the generator will not do Zero Copying of strings, as most
-// third party libraries do not follow Apple's design guidelines of making
-// string properties and parameters copy parameters, instead many libraries
-// "retain" as a broken optimization [1].
-//
-// The consumer of the generator can force this by passing
-// --use-zero-copy or setting the [assembly:ZeroCopyStrings] attribute.
-// When these are set, the generator assumes the library perform
-// copies over any NSStrings it keeps instead of retains/assigns and
-// that any property that happens to be a retain/assign has the
-// [DisableZeroCopyAttribute] attribute applied.
-//
-// [1] It is broken because consumer code can pass an NSMutableString, the
-// library retains the value, but does not have a way of noticing changes
-// that might happen to the mutable string behind its back.
-//
-// In the ZeroCopy case it is a problem because we pass handles to stack-allocated
-// strings that stop existing after the invocation is over.
-//
+#if !XAMCORE_5_0
+// This attribute is obsolete and has no effect. Zero-copy string marshaling is no longer supported.
+[Obsolete ("Zero-copy string marshaling is no longer supported. This attribute has no effect.")]
 [AttributeUsage (AttributeTargets.Assembly | AttributeTargets.Method | AttributeTargets.Interface, AllowMultiple = true)]
 public class ZeroCopyStringsAttribute : Attribute {
 }
+#endif
 
 [AttributeUsage (AttributeTargets.Method | AttributeTargets.Property, AllowMultiple = true)]
 public class SnippetAttribute : Attribute {

diff --git a/src/bgen/BindingTouch.cs b/src/bgen/BindingTouch.cs
@@ -163,7 +163,9 @@ public bool TryCreateOptionSet (BindingTouchConfig config, string [] args)
 				{ "p", "Sets private mode", v => config.IsPublicMode = false },
 				{ "baselib=", "Sets the base library", v => config.Baselibdll = v },
 				{ "attributelib=", "Sets the attribute library", v => config.Attributedll = v },
-				{ "use-zero-copy", v=> config.UseZeroCopy = true },
+#if !XAMCORE_5_0
+				{ "use-zero-copy", v=> ErrorHelper.Warning (1027) },
+#endif
 				{ "nostdlib", "Does not reference mscorlib.dll library", l => config.OmitStandardLibrary = true },
 #if !XAMCORE_5_0
 				{ "no-mono-path", "Launches compiler with empty MONO_PATH", l => { }, true },
@@ -364,7 +366,6 @@ bool TryGenerate (BindingTouchConfig config, Api api)
 		try {
 			var g = new Generator (this, api, config.IsPublicMode, config.IsExternal, config.IsDebug) {
 				BaseDir = config.BindingFilesOutputDirectory ?? config.TemporaryFileDirectory!,
-				ZeroCopyStrings = config.UseZeroCopy,
 				InlineSelectors = config.InlineSelectors ?? (CurrentPlatform != PlatformName.MacOSX),
 			};
 

diff --git a/src/bgen/Generator.cs b/src/bgen/Generator.cs
@@ -109,9 +109,6 @@ Nomenclator Nomenclator {
 	string? is_direct_binding_value; // An expression that calculates the IsDirectBinding value. Might not be a constant expression. This will be added to every constructor for a type.
 	bool? is_direct_binding; // If a constant value for IsDirectBinding is known, it's stored here. Will be null if no constant value is known.
 
-	// Whether to use ZeroCopy for strings, defaults to false
-	public bool ZeroCopyStrings;
-
 	public bool BindThirdPartyLibrary { get { return BindingTouch.BindThirdPartyLibrary; } }
 	public bool InlineSelectors;
 	public string BaseDir { get { return basedir; } set { basedir = value; } }
@@ -124,11 +121,6 @@ Nomenclator Nomenclator {
 	//
 	bool type_needs_thread_checks;
 
-	//
-	// If set, the members of this type will get zero copy
-	// 
-	internal bool type_wants_zero_copy;
-
 	//
 	// Used by the public binding generator to populate the
 	// class with types that do not exist
@@ -843,16 +835,7 @@ public TrampolineInfo MakeTrampoline (Type t)
 			if (mai.PlainString)
 				return safe_name;
 			else {
-				bool allow_null = null_allowed_override || AttributeManager.IsNullable (pi);
-
-				if (mai.ZeroCopyStringMarshal) {
-					if (allow_null)
-						return String.Format ("{0} is null ? IntPtr.Zero : (IntPtr)(&_s{0})", pi.Name);
-					else
-						return String.Format ("(IntPtr)(&_s{0})", pi.Name);
-				} else {
-					return "ns" + pi.Name;
-				}
+				return "ns" + pi.Name;
 			}
 		}
 
@@ -3097,13 +3080,8 @@ void GenerateInvoke (bool stret, bool supercall, MethodInfo mi, MemberInformatio
 						if (mai.PlainString)
 							ErrorHelper.Warning (1101);
 
-						if (mai.ZeroCopyStringMarshal) {
-							target_name = "(IntPtr)(&_s" + pi.Name + ")";
-							handle = "";
-						} else {
-							target_name = "ns" + pi.Name;
-							handle = "";
-						}
+						target_name = "ns" + pi.Name;
+						handle = "";
 					} else
 						target_name = pi.Name.GetSafeParamName ();
 					break;
@@ -3248,48 +3226,16 @@ bool IsOptimizable (MemberInfo method)
 	// @probe_null: determines whether null is allowed, and
 	// whether we need to generate code to handle this
 	//
-	// @must_copy: determines whether to create a new NSString, necessary
-	// for NSString properties that are flagged with "retain" instead of "copy"
-	//
-	// @prefix: prefix to prepend on each line
-	//
 	// @property: the name of the property
 	//
-	public string GenerateMarshalString (bool probe_null, bool must_copy)
-	{
-		if (must_copy) {
-			return "var ns{0} = CFString.CreateNative ({1});\n";
-		}
-		return
-			"ObjCRuntime.NSStringStruct _s{0}; Console.WriteLine (\"" + CurrentMethod + ": Marshalling: {{1}}\", {1}); \n" +
-			"_s{0}.ClassPtr = ObjCRuntime.NSStringStruct.ReferencePtr;\n" +
-			"_s{0}.Flags = 0x010007d1; // RefCount=1, Unicode, InlineContents = 0, DontFreeContents\n" +
-			"_s{0}.UnicodePtr = _p{0};\n" +
-			"_s{0}.Length = " + (probe_null ? "{1} is null ? 0 : {1}.Length;" : "{1}.Length;\n");
-	}
-
-	public string GenerateDisposeString (bool probe_null, bool must_copy)
+	public string GenerateMarshalString (bool probe_null)
 	{
-		if (must_copy) {
-			return "CFString.ReleaseNative (ns{0});\n";
-		} else
-			return "if (_s{0}.Flags != 0x010007d1) throw new Exception (\"String was retained, not copied\");";
+		return "var ns{0} = CFString.CreateNative ({1});\n";
 	}
 
-	List<string>? CollectFastStringMarshalParameters (MethodInfo mi)
+	public string GenerateDisposeString (bool probe_null)
 	{
-		List<string>? stringParameters = null;
-
-		foreach (var pi in mi.GetParameters ()) {
-			var mai = new MarshalInfo (this, mi, pi);
-
-			if (mai.ZeroCopyStringMarshal) {
-				if (stringParameters is null)
-					stringParameters = new List<string> ();
-				stringParameters.Add (pi.Name.GetSafeParamName () ?? "");
-			}
-		}
-		return stringParameters;
+		return "CFString.ReleaseNative (ns{0});\n";
 	}
 
 	AvailabilityBaseAttribute? GetIntroduced (Type? type, string methodName)
@@ -3371,8 +3317,8 @@ void GenerateTypeLowering (MethodInfo mi, bool null_allowed_override, out String
 			if (mai.Type == TypeCache.System_String && !mai.PlainString) {
 				bool probe_null = null_allowed_override || AttributeManager.IsNullable (pi);
 
-				convs.AppendFormat (GenerateMarshalString (probe_null, !mai.ZeroCopyStringMarshal), pi.Name, pi.Name.GetSafeParamName ());
-				disposes.AppendFormat (GenerateDisposeString (probe_null, !mai.ZeroCopyStringMarshal), pi.Name);
+				convs.AppendFormat (GenerateMarshalString (probe_null), pi.Name, pi.Name.GetSafeParamName ());
+				disposes.AppendFormat (GenerateDisposeString (probe_null), pi.Name);
 			} else if (mai.Type.TryIsArray (out var etype)) {
 				if (HasBindAsAttribute (pi)) {
 					convs.AppendFormat ("using var nsb_{0} = {1}\n", pi.Name, GetToBindAsWrapper (mi, null, pi));
@@ -3615,9 +3561,6 @@ public void GenerateMethodBody (MemberInformation minfo, MethodInfo mi, string?
 
 		GenerateArgumentChecks (mi, false, propInfo, out bool needsGCKeepAlives);
 
-		// Collect all strings that can be fast-marshalled
-		var stringParameters = CollectFastStringMarshalParameters (mi);
-
 		GenerateTypeLowering (mi, null_allowed_override, out var args, out var convs, out var disposes, out var by_ref_processing, out var by_ref_init, out var post_return, propInfo);
 
 		if (minfo.is_protocol_member && minfo.is_static) {
@@ -3629,12 +3572,6 @@ public void GenerateMethodBody (MemberInformation minfo, MethodInfo mi, string?
 		if (by_ref_init.Length > 0)
 			print (by_ref_init.ToString ());
 
-		if (stringParameters is not null) {
-			print ("fixed (char * {0}){{",
-				  stringParameters.Select (name => "_p" + name + " = " + name).Aggregate ((first, second) => first + ", " + second));
-			indent++;
-		}
-
 		if (propInfo is not null && IsSetter (mi) && HasBindAsAttribute (propInfo)) {
 			convs.AppendFormat ("using var nsb_{0} = {1}\n", propInfo.Name, GetToBindAsWrapper (mi, minfo, null));
 		}
@@ -3834,10 +3771,6 @@ public void GenerateMethodBody (MemberInformation minfo, MethodInfo mi, string?
 			WriteMarkDirtyIfDerived (sw, mi.DeclaringType!);
 		if (post_return?.Length > 0)
 			print (post_return.ToString ());
-		if (stringParameters is not null) {
-			indent--;
-			print ("}");
-		}
 		indent--;
 	}
 
@@ -5769,12 +5702,6 @@ public void Generate (Type type)
 		if (is_rgen_type)
 			return;
 
-		if (ZeroCopyStrings) {
-			ErrorHelper.Warning (1027);
-			ZeroCopyStrings = false;
-		}
-
-		type_wants_zero_copy = AttributeManager.HasAttribute<ZeroCopyStringsAttribute> (type) || ZeroCopyStrings;
 		var tsa = AttributeManager.GetCustomAttribute<ThreadSafeAttribute> (type);
 		// if we're inside a special namespace then default is non-thread safe, otherwise default is thread safe
 		if (NamespaceCache.UINamespaces.Contains (type.Namespace!)) {

diff --git a/src/bgen/Models/BindingTouchConfig.cs b/src/bgen/Models/BindingTouchConfig.cs
@@ -5,7 +5,6 @@
 
 public class BindingTouchConfig {
 	public bool ShowHelp = false;
-	public bool UseZeroCopy = false;
 	public string? BindingFilesOutputDirectory = null;
 	public string? TemporaryFileDirectory = null;
 	public string? HelperClassNamespace = null;