ZeroAlloc.Specification

Source-generated specification pattern for .NET, an Ardalis.Specification alternative: specs are structs, so composing and evaluating them allocates nothing, and the same spec still translates to SQL through EF Core.

Why ZeroAlloc.Specification

• Composing and evaluating allocates nothing. And, Or and Not build readonly struct values. Composing and calling IsSatisfiedBy allocates 0 B, asserted by tests. Ardalis.Specification allocates 1,752 B to compose two specs.
• About 320× faster for in-memory filtering than Ardalis.Specification, measured in the same run: 100 items in 49 ns instead of 15,599 ns, because nothing is compiled per call.
• One spec for memory and the database. Every spec also exposes ToExpression(), so EF Core turns the composed spec into a WHERE clause.
• Works under NativeAOT and trimming, with a NativeAOT smoke app published and run in CI. Mistakes such as [Specification] on a class or a missing partial are compile errors ZA001 to ZA003.

Install

dotnet add package ZeroAlloc.Specification

The source generator ships inside this package. Targets .NET 8 and later.

Quick start

using System.Linq.Expressions;
using ZeroAlloc.Specification;

User[] users = [new("Ann", true, 1500m), new("Bob", true, 200m), new("Cy", false, 3000m)];

var spec = new ActiveUserSpec().And(new BigSpenderSpec(1000m));        // a struct, 0 B

Console.WriteLine(users.Count(u => spec.IsSatisfiedBy(u)));             // 1, in memory
Console.WriteLine(spec.ToExpression());   // one combined expression for dbContext.Users.Where(...)

public sealed record User(string Name, bool IsActive, decimal TotalSpend);

[Specification]
public readonly partial struct ActiveUserSpec : ISpecification<User>
{
    public bool IsSatisfiedBy(User user) => user.IsActive;
    public Expression<Func<User, bool>> ToExpression() => u => u.IsActive;
}

[Specification]
public readonly partial struct BigSpenderSpec(decimal minSpend) : ISpecification<User>
{
    public bool IsSatisfiedBy(User user) => user.TotalSpend >= minSpend;
    public Expression<Func<User, bool>> ToExpression() { var min = minSpend; return u => u.TotalSpend >= min; }
}

The generator adds And, Or and Not to every [Specification] struct. Evaluation is a direct call on a struct that the JIT can inline, with no virtual dispatch.

What you get

• Fluent composition: And, Or and Not, nested to any depth, without allocating.
• Static builder: Spec.And, Spec.Or and Spec.Not when you want explicit type arguments.
• In-memory evaluation through IsSatisfiedBy, for hot loops and domain rules.
• EF Core translation through ToExpression(), which combines the specs' expression trees into one.
• Compile-time checks that each spec is a readonly partial struct implementing ISpecification<T>.
• Recipes for an EF Core repository, complex compositions and caching the expression of a stateless spec.

Building an expression tree with ToExpression() does allocate, as every expression tree does. Cache it for stateless specs.

Performance

Head-to-head vs Ardalis.Specification 9.3.1, .NET 10.0.13, BenchmarkDotNet v0.15.8.

Operation	Ardalis.Specification	ZA.Specification	Speedup
Construct composed spec	305 ns / 792 B	< 1 ns / 0 B	> 300× faster, 0 B alloc
Compose two specs	821 ns / 1,752 B	< 1 ns / 0 B	> 800× faster, 0 B alloc
Evaluate over 100 items (in-memory)	15,599 ns / 4,743 B	49 ns / 0 B	~320× faster, 0 B alloc

Rows under 1 ns are below what BenchmarkDotNet can tell apart from an empty method, so those speedups are lower bounds. The machine was shared while measuring, so timings are approximate; the allocations are exact. For database queries the SQL provider dominates and the gap is invisible; for in-memory filtering it dominates. Full methodology: docs/performance.md.

Learn more

• Documentation: specification.zeroalloc.net. Start with getting started, core concepts and the diagnostics reference.
• Release history: CHANGELOG.md.
• More ZeroAlloc libraries, such as ZeroAlloc.Validation and ZeroAlloc.Mapping: zeroalloc.net.
• Issues and pull requests are welcome on GitHub.
• MIT licensed. See LICENSE.