BunnyTail.MemberAccessor

AOT-safe source-generated member accessor for .NET. A reflection-free alternative for property get/set, constructor invocation, and member enumeration.

Support Matrix

Feature	Supported	Notes
class	✅	Full support
struct	✅	Boxed instance required for IAccessor.SetValue; typed CreateSetter<T> returns null (see Struct Support)
record (class)	✅	Treated as class
record struct	✅	Treated as struct
Open generic (Foo<T>)	✅	On-demand closed-type instantiation
Closed generic pre-registration	✅	[TypedAccessor(typeof(Foo<int>))]
Inherited properties	✅	Flattened from base classes
Public instance properties	✅	Read/write; static, non-public and indexers are ignored
Read-only properties	✅	Setter returns null
Constructor accessor	✅	Arity 0–4; AOT-safe; generic types supported
Same-arity constructor overloads	✅	Resolved by argument type at runtime (see Constructor Accessor)
IAccessorFactory.Members	✅	IReadOnlyList<MemberDescriptor> (public instance properties only)
static members	❌	Not yet supported
Non-public members	❌	Public only
Fields	❌	Properties only
init-only properties	✅	Readable; init setters are treated as read-only (CanWrite = false, typed setter returns null)

Reference

Add reference to BunnyTail.MemberAccessor to csproj.

  <ItemGroup>
    <PackageReference Include="BunnyTail.MemberAccessor" Version="1.2.0" />
  </ItemGroup>

MemberAccessor

Source

using BunnyTail.MemberAccessor;

[GenerateAccessor]
public class Data
{
    public int Id { get; set; }

    public string Name { get; set; } = default!;
}

using BunnyTail.MemberAccessor;

var accessorFactory = AccessorRegistry.FindFactory<Data>();
var getter = accessorFactory.CreateGetter<int>(nameof(Data.Id));
var setter = accessorFactory.CreateSetter<int>(nameof(Data.Id));

var data = new Data();
setter(data, 123);
var id = getter(data);

Member Enumeration

var factory = AccessorRegistry.FindFactory<Data>();
foreach (var member in factory.Members)
{
    Console.WriteLine($"{member.Name}: {member.Type} CanRead={member.CanRead} CanWrite={member.CanWrite}");
}

Constructor Accessor

var ctor = AccessorRegistry.FindConstructor<Data>();
var instance = ctor.Create();          // parameterless
var instance2 = ctor.Create<int>(42); // 1-arg constructor

Constructor accessors are available for generic types as well (closed types are pre-registered with [TypedAccessor], others are created on demand):

var ctor = AccessorRegistry.FindConstructor<GenericHolder<int>>();
var instance = ctor.Create<int>(42);

When a type declares multiple constructors with the same arity, the matching constructor is selected at runtime by the argument type. Pass the exact parameter type as the type argument:

// class Sample { Sample(int v); Sample(string v); }
var ctor = AccessorRegistry.FindConstructor<Sample>();
var a = ctor.Create(42);      // -> Sample(int)
var b = ctor.Create("text");  // -> Sample(string)

If no constructor matches the supplied argument type, NotSupportedException is thrown.

Struct Support

[GenerateAccessor]
public struct Point { public int X { get; set; } public int Y { get; set; } }

var accessor = AccessorRegistry.FindAccessor<Point>();
object boxed = new Point { X = 1, Y = 2 };
accessor.SetValue(boxed, "X", 10); // modifies boxed instance

Note: For value types, the typed IAccessorFactory<T>.CreateSetter<TProperty> returns null, because a delegate void(T, TProperty) would receive a copy of the struct and could not mutate the caller's value. Use IAccessor.SetValue with a boxed instance to modify a struct.

Benchmark

BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.7171/25H2/2025Update/HudsonValley2)
AMD Ryzen 9 5900X 3.70GHz, 1 CPU, 24 logical and 12 physical cores
.NET SDK 10.0.100
  [Host]    : .NET 10.0.0 (10.0.0, 10.0.25.52411), X64 RyuJIT x86-64-v3
  MediumRun : .NET 10.0.0 (10.0.0, 10.0.25.52411), X64 RyuJIT x86-64-v3

Job=MediumRun  IterationCount=15  LaunchCount=2  
WarmupCount=10  

Method	Mean	Error	StdDev	Min	Max	P90	Code Size	Gen0	Allocated
DirectGetter	0.2243 ns	0.0064 ns	0.0095 ns	0.2138 ns	0.2538 ns	0.2375 ns	10 B	-	-
PropertyGetter	20.6895 ns	0.5456 ns	0.8166 ns	19.6389 ns	22.6418 ns	21.8329 ns	3,019 B	0.0014	24 B
PropertyGetterCashed	8.9811 ns	0.2230 ns	0.3338 ns	8.5007 ns	9.7118 ns	9.3515 ns	3,278 B	0.0014	24 B
AccessorGetter	10.6687 ns	0.2781 ns	0.4163 ns	9.9247 ns	11.7124 ns	11.1563 ns	3,219 B	0.0014	24 B
AccessorGetterCached	2.3157 ns	0.0976 ns	0.1461 ns	2.0956 ns	2.5933 ns	2.4920 ns	174 B	0.0014	24 B
ExpressionGetter	1.3618 ns	0.0267 ns	0.0392 ns	1.2959 ns	1.4362 ns	1.4167 ns	54 B	-	-
GeneratorGetter	0.2304 ns	0.0055 ns	0.0082 ns	0.2172 ns	0.2518 ns	0.2416 ns	76 B	-	-
DirectSetter	0.2291 ns	0.0066 ns	0.0099 ns	0.2145 ns	0.2458 ns	0.2427 ns	28 B	-	-
PropertySetter	19.3523 ns	0.6403 ns	0.9584 ns	17.8336 ns	21.3628 ns	20.3991 ns	8,536 B	0.0014	24 B
PropertySetterCashed	11.1574 ns	0.2706 ns	0.4051 ns	10.5017 ns	11.5931 ns	11.5931 ns	8,736 B	0.0014	24 B
AccessorSetter	10.5961 ns	0.2128 ns	0.3120 ns	10.1118 ns	11.3181 ns	11.0217 ns	3,238 B	0.0014	24 B
AccessorSetterCached	2.2665 ns	0.1085 ns	0.1623 ns	1.9878 ns	2.5154 ns	2.4811 ns	191 B	0.0014	24 B
ExpressionSetter	1.4610 ns	0.0427 ns	0.0599 ns	1.3909 ns	1.6234 ns	1.5634 ns	57 B	-	-
GeneratorSetter	0.5057 ns	0.0181 ns	0.0259 ns	0.4630 ns	0.5806 ns	0.5321 ns	85 B	-	-

Type Scenarios

Cached reflection (PropertyInfo) compared with the generated typed accessor (CreateGetter<T> / CreateSetter<T>) across property types (int / string), a value type (struct), a large class, and a generic type. The generated accessor is allocation-free and stays roughly constant regardless of the member type or the declaring-type kind.

BenchmarkDotNet v0.15.8, Windows 11 (10.0.26200.8524/25H2/2025Update/HudsonValley2)
AMD Ryzen 9 5900X 3.70GHz, 1 CPU, 24 logical and 12 physical cores
.NET SDK 10.0.300
  [Host]    : .NET 10.0.8 (10.0.8, 10.0.826.23019), X64 RyuJIT x86-64-v3
  MediumRun : .NET 10.0.8 (10.0.8, 10.0.826.23019), X64 RyuJIT x86-64-v3

Job=MediumRun  IterationCount=15  LaunchCount=2  
WarmupCount=10  

Method	Mean	Error	StdDev	Min	Max	P90	Gen0	Allocated
IntGetReflection	11.2540 ns	0.5883 ns	0.8805 ns	10.1597 ns	13.0197 ns	12.3929 ns	0.0014	24 B
IntGetGenerator	0.2751 ns	0.0052 ns	0.0074 ns	0.2604 ns	0.2916 ns	0.2840 ns	-	-
IntSetReflection	13.5897 ns	0.6378 ns	0.9147 ns	12.6522 ns	16.0574 ns	15.0835 ns	0.0014	24 B
IntSetGenerator	0.2780 ns	0.0108 ns	0.0158 ns	0.2614 ns	0.3194 ns	0.3024 ns	-	-
StringGetReflection	7.5344 ns	0.1788 ns	0.2620 ns	7.0083 ns	8.1777 ns	7.9011 ns	-	-
StringGetGenerator	0.3142 ns	0.0236 ns	0.0354 ns	0.2700 ns	0.3841 ns	0.3574 ns	-	-
StringSetReflection	12.0234 ns	0.3071 ns	0.4597 ns	11.3507 ns	13.1734 ns	12.6080 ns	-	-
StringSetGenerator	0.2908 ns	0.0139 ns	0.0203 ns	0.2281 ns	0.3274 ns	0.3096 ns	-	-
StructGetReflection	10.7348 ns	0.3399 ns	0.4765 ns	9.9749 ns	11.7202 ns	11.3857 ns	0.0014	24 B
StructGetGenerator	0.3123 ns	0.0291 ns	0.0435 ns	0.2205 ns	0.3754 ns	0.3677 ns	-	-
LargeGetReflection	10.3250 ns	0.3926 ns	0.5631 ns	9.7004 ns	11.8913 ns	11.1991 ns	0.0014	24 B
LargeGetGenerator	0.2837 ns	0.0225 ns	0.0315 ns	0.2514 ns	0.3526 ns	0.3394 ns	-	-
LargeSetReflection	13.8748 ns	0.8492 ns	1.2448 ns	12.8041 ns	17.1278 ns	16.1829 ns	0.0014	24 B
LargeSetGenerator	0.2960 ns	0.0183 ns	0.0274 ns	0.2682 ns	0.3671 ns	0.3377 ns	-	-
GenericGetReflection	11.0396 ns	0.6136 ns	0.8995 ns	10.0449 ns	13.5371 ns	12.5900 ns	0.0014	24 B
GenericGetGenerator	0.2951 ns	0.0177 ns	0.0265 ns	0.2712 ns	0.3638 ns	0.3351 ns	-	-
GenericSetReflection	13.9884 ns	0.4783 ns	0.7010 ns	12.9126 ns	15.8474 ns	14.8361 ns	0.0014	24 B
GenericSetGenerator	0.2836 ns	0.0035 ns	0.0049 ns	0.2683 ns	0.2925 ns	0.2884 ns	-	-