MulticastFunc

MulticastFunc is a high-performance, drop-in alternative to Func that retrieves the return values of all invocations instead of only the final one.

The Problem

To collect results from all targets in a standard .NET MulticastDelegate, you have to extract the invocation list manually:

T[]? results = myDelegate?.GetInvocationList().Cast<Func<T>>().Select(f => f.Invoke()).ToArray();

Even when hidden behind an extension method, the allocation cost of GetInvocationList() cannot be avoided. This approach is slow and generates unnecessary garbage.

The Solution: MulticastFunc solves this by returning an array of all results directly from Invoke() while matching native delegate performance. See Benchmarks.

Features

• Familiar Syntax: Implements standard add/remove (+= / -=) operator behavior.
• Thread-Safe: Immutable design guarantees safe concurrent execution.
• Allocation-Free Overloads: Supports writing return values to a Span buffer.
• Fault Tolerance: Optional execution path runs all delegates regardless of individual errors, throwing an aggregated exception at the end.
• Native AOT: Native AOT compilation and trim compatible.

Installation

dotnet add package MulticastFunc

Requirements: .NET Standard 2.1 or newer

Usage Examples

Basic Mechanics

// Subscription
multicastFunc += MyMethod;
multicastFunc += () => "Hello World";

// Standard Invocation
string[]? results = multicastFunc?.Invoke();

Event Backing Field

public event Func<string> EventHappened
{
    add => multicastFunc += value;
    remove => multicastFunc -= value;
}
private MulticastFunc<string>? multicastFunc = default;

Advanced Execution Modes

// Fault-Tolerant: Invokes everything. Failing targets return default(T). Throws AggregateException.
string[]? results = multicastFunc?.InvokeAll();

// Allocation-Free: Write to a Span buffer for hot paths.
var buffer = ArrayPool<string>.Shared.Rent(multicastFunc.Count);
ReadOnlySpan<string> results = multicastFunc.Invoke(buffer);

Technical Limitations

• Subscription Overhead: MulticastFunc is immutable to match the behavior of standard delegates. As a result, subscribing (+) generates more garbage than native delegates.
• No Direct Method Group Assignments: The compiler does not recognize MulticastFunc as a native delegate type. As a result, direct assignment from a method group multicastFunc = MyMethod is invalid; you must use compounding assignment multicastFunc += MyMethod.

Benchmarks (.NET 8)

MulticastFunc.Invoke() performs on par with a raw Func.Invoke() and runs ~6 times faster than equivalent LINQ invocations.

Invocation Performance

| Method | DelegateCount | Mean | Ratio | Allocated | |——————————– |————– |————-:|——:|———-:| | Invoke_MulticastFunc | 5 | 13.783 ns | 1.13 | 48 B | | Invoke_MulticastFunc_SpanBuffer | 5 | 8.630 ns | 0.71 | - | | Invoke_Func_LastResultOnly | 5 | 12.171 ns | 1.00 | - | | Invoke_Func_Linq | 5 | 103.306 ns | 8.49 | 352 B | | | | | | | | Invoke_MulticastFunc | 25 | 50.962 ns | 0.91 | 128 B | | Invoke_MulticastFunc_SpanBuffer | 25 | 38.537 ns | 0.69 | - | | Invoke_Func_LastResultOnly | 25 | 56.183 ns | 1.00 | - | | Invoke_Func_Linq | 25 | 336.678 ns | 5.99 | 792 B | | | | | | | | Invoke_MulticastFunc | 125 | 230.311 ns | 0.83 | 528 B | | Invoke_MulticastFunc_SpanBuffer | 125 | 187.109 ns | 0.68 | - | | Invoke_Func_LastResultOnly | 125 | 276.251 ns | 1.00 | - | | Invoke_Func_Linq | 125 | 1,394.755 ns | 5.05 | 2424 B |

Subscription Performance (+=)

| Method | DelegateCount | Mean | Ratio | Gen1 | Allocated | Alloc Ratio | |———————— |————– |———:|——:|——-:|———-:|————:| | Subscribe_Func | 5 | 20.14 ns | 1.00 | - | 64 B | 1.00 | | Subscribe_MulticastFunc | 5 | 17.51 ns | 0.87 | - | 128 B | 2.00 | | | | | | | | | | Subscribe_Func | 25 | 20.29 ns | 1.00 | - | 64 B | 1.00 | | Subscribe_MulticastFunc | 25 | 21.58 ns | 1.06 | - | 288 B | 4.50 | | | | | | | | | | Subscribe_Func | 125 | 20.52 ns | 1.00 | - | 64 B | 1.00 | | Subscribe_MulticastFunc | 125 | 39.93 ns | 1.95 | 0.0002 | 1088 B | 17.00 |

Unsubscription Performance (-=)

| Method | DelegateCount | Mean | Ratio | Gen1 | Allocated | Alloc Ratio | |————————– |————– |———-:|——:|——-:|———-:|————:| | Unsubscribe_Func | 5 | 24.98 ns | 1.00 | - | 120 B | 1.00 | | Unsubscribe_MulticastFunc | 5 | 18.09 ns | 0.72 | - | 112 B | 0.93 | | | | | | | | | | Unsubscribe_Func | 25 | 46.11 ns | 1.00 | - | 344 B | 1.00 | | Unsubscribe_MulticastFunc | 25 | 23.02 ns | 0.50 | - | 272 B | 0.79 | | | | | | | | | | Unsubscribe_Func | 125 | 148.88 ns | 1.00 | 0.0002 | 1112 B | 1.00 | | Unsubscribe_MulticastFunc | 125 | 39.29 ns | 0.26 | 0.0002 | 1072 B | 0.96 |

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