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Getting Started

Installation​

dotnet add package ZeroAlloc.Specification
dotnet add package ZeroAlloc.Specification.Generator
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The generator package is a Roslyn analyzer/source generator. It is automatically applied at compile time — no runtime dependency.

Your First Specification​

1. Define a spec struct​

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

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

The [Specification] attribute and partial keyword are both required. The generator adds fluent composition methods to your struct.

2. Use it in memory​

var spec = new ActiveUserSpec();
bool result = spec.IsSatisfiedBy(user); // true/false

3. Compose specifications​

[Specification]
public readonly partial struct PremiumUserSpec : ISpecification<User>
{
    private readonly decimal _minSpend;
    public PremiumUserSpec(decimal minSpend) => _minSpend = minSpend;

    public bool IsSatisfiedBy(User user) => user.TotalSpend >= _minSpend;
    public Expression<Func<User, bool>> ToExpression()
    {
        var min = _minSpend; // copy field to local for lambda capture
        return u => u.TotalSpend >= min;
    }
}

// Fluent:
var spec = new ActiveUserSpec().And(new PremiumUserSpec(1000m));

// Static builder:
var spec = Spec.And<ActiveUserSpec, PremiumUserSpec, User>(new(), new(1000m));

Both produce AndSpecification<ActiveUserSpec, PremiumUserSpec, User> — a struct, zero heap allocation.

4. Query with EF Core​

var users = await dbContext.Users
    .Where(spec.ToExpression())
    .ToListAsync();

EF Core translates the composed expression tree to SQL.

Next Steps​