feat: AOT compatibility - move collection properties to extension methods

Move Array, Array2D, List, HashSet, and ArrayUnique from Gen<T> instance
properties to extension methods on the static Gen class. This prevents
infinite generic type expansion during NativeAOT compilation (ILC) when
Gen<T> is instantiated for self-referential types.

BREAKING CHANGE: .Array, .Array2D, .List, .HashSet, .ArrayUnique are now
methods requiring parentheses: .Array(), .Array2D(), .List(), .HashSet(),
.ArrayUnique(). Indexer syntax is unchanged: .Array()[0, 5].

- Add IsAotCompatible to CsCheck.csproj
- Update all call sites in library, tests, and documentation
- Verified: 299 tests pass, NativeAOT compiles including recursive types

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: AnthonyLloyd

CsCheck/Check.cs

@@ -1,4 +1,4 @@
-// Copyright 2026 Anthony Lloyd
+// Copyright 2026 Anthony Lloyd
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -1408,7 +1408,7 @@ public static void SampleModelBased<Actual, Model>(this Gen<(Actual, Model)> ini
         }
 
         new GenInitial<Actual, Model>(initial)
-        .Select(Gen.OneOf(opNameActions).Array, (a, b) => new ModelBasedData<Actual, Model>(a.Actual, a.Model, a.Stream, a.Seed, b))
+        .Select(Gen.OneOf(opNameActions).Array(), (a, b) => new ModelBasedData<Actual, Model>(a.Actual, a.Model, a.Stream, a.Seed, b))
         .Sample(d =>
         {
             try
@@ -1754,7 +1754,7 @@ public static void SampleParallel<T>(this Gen<T> initial, GenOperation<T>[] oper
         Gen.Int[2, maxParallelOperations]
         .SelectMany(np => Gen.Int[2, Math.Min(threads, np)].Select(nt => (nt, np)))
         .SelectMany((nt, np) => Gen.Int[0, maxSequentialOperations].Select(ns => (ns, nt, np)))
-        .SelectMany((ns, nt, np) => new GenSampleParallel<T>(initial).Select(genOps.Array[ns], genOps.Array[np])
+        .SelectMany((ns, nt, np) => new GenSampleParallel<T>(initial).Select(genOps.Array()[ns], genOps.Array()[np])
                                     .Select((initial, sequential, parallel) => (initial, sequential, nt, parallel)))
         .Select((initial, sequential, threads, parallel) => new SampleParallelData<T>(initial.Value, initial.Stream, initial.Seed, sequential, parallel, threads))
         .Sample(spd =>
@@ -2018,7 +2018,7 @@ public static void SampleParallel<Actual, Model>(this Gen<(Actual, Model)> initi
         Gen.Int[2, maxParallelOperations]
         .SelectMany(np => Gen.Int[2, Math.Min(threads, np)].Select(nt => (nt, np)))
         .SelectMany((nt, np) => Gen.Int[0, maxSequentialOperations].Select(ns => (ns, nt, np)))
-        .SelectMany((ns, nt, np) => new GenSampleParallel<Actual, Model>(initial).Select(genOps.Array[ns], genOps.Array[np])
+        .SelectMany((ns, nt, np) => new GenSampleParallel<Actual, Model>(initial).Select(genOps.Array()[ns], genOps.Array()[np])
                                     .Select((initial, sequential, parallel) => (initial, sequential, nt, parallel)))
         .Select((initial, sequential, threads, parallel) => new SampleParallelData<Actual, Model>(initial.Actual, initial.Model, initial.Stream, initial.Seed, sequential, parallel, threads))
         .Sample(spd =>

CsCheck/CsCheck.csproj

@@ -44,6 +44,7 @@ Fixed Faster statistics locking.
         <NoWarn>CS1591,MA0143</NoWarn>
         <PackageReadmeFile>README.md</PackageReadmeFile>
         <AnalysisMode>All</AnalysisMode>
+        <IsAotCompatible>true</IsAotCompatible>
     </PropertyGroup>
     <ItemGroup>
         <PackageReference Include="Microsoft.SourceLink.GitHub" Version="10.0.103" PrivateAssets="All" />

CsCheck/Gen.cs

@@ -1,4 +1,4 @@
-// Copyright 2026 Anthony Lloyd
+// Copyright 2026 Anthony Lloyd
 // 
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -91,24 +91,24 @@ public abstract class Gen<T> : IGen<T>
     public GenOperation<Actual, Model> Operation<Actual, Model>(Action<Actual, T> actual, Action<Model, T> model) => GenOperation.Create(this, actual, model);
     public GenMetamorphic<S> Metamorphic<S>(Func<T, string> name, Action<S, T> action1, Action<S, T> action2) => GenMetamorphic.Create(this, name, action1, action2);
     public GenMetamorphic<S> Metamorphic<S>(Action<S, T> action1, Action<S, T> action2) => GenMetamorphic.Create(this, Check.Print, action1, action2);
-
-    /// <summary>Generator for an array of <typeparamref name="T"/></summary>
-    public GenArray<T> Array => new(this);
-    /// <summary>Generator for a two dimensional array of <typeparamref name="T"/></summary>
-    public GenArray2D<T> Array2D => new(this);
-    /// <summary>Generator for a List of <typeparamref name="T"/></summary>
-    public GenList<T> List => new(this);
-    /// <summary>Generator for a HashSet of <typeparamref name="T"/></summary>
-    public GenHashSet<T> HashSet => new(this);
-    /// <summary>Generator for a unique array of <typeparamref name="T"/></summary>
-    public GenArrayUnique<T> ArrayUnique => new(this);
 }
 
 public delegate T GenMap<T>(T v, ref Size size);
 
 /// <summary>Provides a set of static methods for composing generators.</summary>
 public static class Gen
 {
+    /// <summary>Generator for an array of <typeparamref name="T"/></summary>
+    public static GenArray<T> Array<T>(this Gen<T> gen) => new(gen);
+    /// <summary>Generator for a two dimensional array of <typeparamref name="T"/></summary>
+    public static GenArray2D<T> Array2D<T>(this Gen<T> gen) => new(gen);
+    /// <summary>Generator for a List of <typeparamref name="T"/></summary>
+    public static GenList<T> List<T>(this Gen<T> gen) => new(gen);
+    /// <summary>Generator for a HashSet of <typeparamref name="T"/></summary>
+    public static GenHashSet<T> HashSet<T>(this Gen<T> gen) => new(gen);
+    /// <summary>Generator for a unique array of <typeparamref name="T"/></summary>
+    public static GenArrayUnique<T> ArrayUnique<T>(this Gen<T> gen) => new(gen);
+
     sealed class GenConst<T>(T value) : Gen<T>
     {
         public override T Generate(PCG pcg, Size? min, out Size size)
@@ -2683,7 +2683,7 @@ public override char Generate(PCG pcg, Size? min, out Size size)
 
 public sealed class GenString : Gen<string>
 {
-    static readonly Gen<string> d = Gen.Char.Array.Select(i => new string(i));
+    static readonly Gen<string> d = Gen.Char.Array().Select(i => new string(i));
     public override string Generate(PCG pcg, Size? min, out Size size)
         => d.Generate(pcg, min, out size);
     /// <summary>Generate string with length in the range <paramref name="start"/> to <paramref name="finish"/> both inclusive.</summary>
@@ -2692,7 +2692,7 @@ public override string Generate(PCG pcg, Size? min, out Size size)
         get
         {
             if (finish < start) ThrowHelper.ThrowFinishLessThanStart(start, finish);
-            return Gen.Char.Array[start, finish].Select(i => new string(i));
+            return Gen.Char.Array()[start, finish].Select(i => new string(i));
         }
     }
 
@@ -2701,16 +2701,16 @@ public override string Generate(PCG pcg, Size? min, out Size size)
         get
         {
             if (finish < start) ThrowHelper.ThrowFinishLessThanStart(start, finish);
-            return gen.Array[start, finish].Select(i => new string(i));
+            return gen.Array()[start, finish].Select(i => new string(i));
         }
     }
 
     public Gen<string> this[Gen<char> gen] =>
-        gen.Array.Select(i => new string(i));
+        gen.Array().Select(i => new string(i));
     /// <summary>Generate string from chars in the string.</summary>
     public Gen<string> this[string chars] =>
-        Gen.Char[chars].Array.Select(i => new string(i));
-    public readonly Gen<string> AlphaNumeric = Gen.Char.AlphaNumeric.Array.Select(i => new string(i));
+        Gen.Char[chars].Array().Select(i => new string(i));
+    public readonly Gen<string> AlphaNumeric = Gen.Char.AlphaNumeric.Array().Select(i => new string(i));
 }
 
 public sealed class GenSeed : Gen<string>

README.md

@@ -35,7 +35,7 @@ The following tests are in ~~xUnit~~ TUnit but could equally be used in any test
 
 More to see in the [Tests](https://github.com/AnthonyLloyd/CsCheck/tree/master/Tests). There are also 1,000+ F# tests using CsCheck in [MKL.NET](https://github.com/MKL-NET/MKL.NET/tree/master/Tests).
 
-No Reflection was used in the making of this product. CsCheck is close to being AOT compatible but 'generic recursion is AOT kryptonite'.
+No Reflection was used in the making of this product. CsCheck is AOT compatible.
 
 ## Generator Creation Example
 
@@ -67,7 +67,7 @@ static readonly Gen<JsonNode> genJsonNode = Gen.Recursive<JsonNode>((depth, genJ
 {
     if (depth == 5) return genJsonValue;
     var genJsonObject = Gen.Dictionary(genString, genJsonNode.Null())[0, 5].Select(d => new JsonObject(d));
-    var genJsonArray = genJsonNode.Null().Array[0, 5].Select(i => new JsonArray(i));
+    var genJsonArray = genJsonNode.Null().Array()[0, 5].Select(i => new JsonArray(i));
     return Gen.OneOf(genJsonObject, genJsonArray, genJsonValue);
 });
 ```
@@ -110,7 +110,7 @@ public void Int_Distribution()
     int buckets = 70;
     int frequency = 10;
     int[] expected = Enumerable.Repeat(frequency, buckets).ToArray();
-    Gen.Int[0, buckets - 1].Array[frequency * buckets]
+    Gen.Int[0, buckets - 1].Array()[frequency * buckets]
     .Select(sample => Tally(buckets, sample))
     .Sample(actual => Check.ChiSquared(expected, actual));
 }
@@ -150,7 +150,7 @@ public void DateTime()
 [Test]
 public void No2_LargeUnionList()
 {
-    Gen.Int.Array.Array
+    Gen.Int.Array().Array()
     .Sample(aa =>
     {
         var hs = new HashSet<int>();
@@ -173,7 +173,7 @@ public void RecursiveDepth()
 {
     int maxDepth = 4;
     Gen.Recursive<MyObj>((i, my) =>
-        Gen.Select(Gen.Int, my.Array[0, i < maxDepth ? 6 : 0], (i, a) => new MyObj(i, a))
+        Gen.Select(Gen.Int, my.Array()[0, i < maxDepth ? 6 : 0], (i, a) => new MyObj(i, a))
     )
     .Sample(i =>
     {
@@ -194,8 +194,8 @@ public void AllocatorMany_Classify()
 {
     Gen.Select(Gen.Int[3, 30], Gen.Int[3, 15]).SelectMany((rows, cols) =>
         Gen.Select(
-            Gen.Int[0, 5].Array[cols].Where(a => a.Sum() > 0).Array[rows],
-            Gen.Int[900, 1000].Array[rows],
+            Gen.Int[0, 5].Array()[cols].Where(a => a.Sum() > 0).Array()[rows],
+            Gen.Int[900, 1000].Array()[rows],
             Gen.Int.Uniform))
     .Sample((solution,
              rowPrice,
@@ -234,7 +234,7 @@ SampleModelBased generates an initial actual and model and then applies a random
 public void
 SetSlim_ModelBased()
 {
-    Gen.Int.Array.Select(a => (new SetSlim<int>(a), new HashSet<int>(a)))
+    Gen.Int.Array().Select(a => (new SetSlim<int>(a), new HashSet<int>(a)))
     .SampleModelBased(
         Gen.Int.Operation<SetSlim<int>, HashSet<int>>(
             (ss, i) => ss.Add(i),
@@ -358,7 +358,7 @@ public void Portfolio_Small_Mixed_Example()
         && p.Positions.Any(p => p.Instrument is Equity)
     , "0N0XIzNsQ0O2");
     var currencies = portfolio.Positions.Select(p => p.Instrument.Currency).Distinct().ToArray();
-    var fxRates = ModelGen.Price.Array[currencies.Length].Single(a =>
+    var fxRates = ModelGen.Price.Array()[currencies.Length].Single(a =>
         a.All(p => pp is > 0.75 and < 1.5)
     , "ftXKwKhS6ec4");
     double fxRate(Currency c) => fxRates[Array.IndexOf(currencies, c)];
@@ -382,7 +382,7 @@ It's just what you need to iteratively improve performance while making sure it
 [Test]
 public void Faster_Linq_Random()
 {
-    Gen.Byte.Array[100, 1000]
+    Gen.Byte.Array()[100, 1000]
     .Faster(
         data => data.Aggregate(0.0, (t, b) => t + b),
         data => data.Select(i => (double)i).Sum(),
@@ -412,7 +412,7 @@ Standard Output Messages:
 public void Faster_Matrix_Multiply_Range()
 {
     var genDim = Gen.Int[5, 30];
-    var genArray = Gen.Double.Unit.Array2D;
+    var genArray = Gen.Double.Unit.Array2D();
     Gen.SelectMany(genDim, genDim, genDim, (i, j, k) => Gen.Select(genArray[i, j], genArray[j, k]))
     .Faster(
         MulIKJ,
@@ -427,7 +427,7 @@ public void Faster_Matrix_Multiply_Range()
 [Test]
 public void MapSlim_Performance_Increment()
 {
-    Gen.Byte.Array
+    Gen.Byte.Array()
     .Select(a => (a, new MapSlim<byte, int>(), new Dictionary<int, int>()))
     .Faster(
         (items, mapslim, _) =>

Tests/AllocatorMany_Tests.cs

@@ -1,4 +1,4 @@
-namespace Tests;
+namespace Tests;
 
 using System;
 using System.Linq;
@@ -10,8 +10,8 @@ public class AllocatorMany_Tests
     public void RoundingSolutionTest()
     {
         Gen.Select(
-            Gen.Int[1, 1000].Array[2, 200],
-            Gen.Int[1, 1000].Select(i => (double)i).Array[2, 20])
+            Gen.Int[1, 1000].Array()[2, 200],
+            Gen.Int[1, 1000].Select(i => (double)i).Array()[2, 20])
         .Sample((rowTotal, colWeight) =>
         {
             var colTotal = Allocator.Allocate(rowTotal.Sum(), colWeight);
@@ -25,8 +25,8 @@ public void GroupUngroup()
     {
         Gen.Select(Gen.Int[2, 10], Gen.Int[2, 10]).SelectMany((I, J) =>
             Gen.Select(
-                Gen.Int[0, 5].Array[J].Where(a => a.Sum() > 0).Array[I],
-                Gen.Int[0, 10].Array[I]))
+                Gen.Int[0, 5].Array()[J].Where(a => a.Sum() > 0).Array()[I],
+                Gen.Int[0, 10].Array()[I]))
         .Sample((solution,
                  rowPrice) =>
         {
@@ -81,8 +81,8 @@ public async Task AllocatorMany_Classify()
     {
         Gen.Select(Gen.Int[3, 30], Gen.Int[3, 15]).SelectMany((rows, cols) =>
             Gen.Select(
-                Gen.Int[0, 5].Array[cols].Where(a => a.Sum() > 0).Array[rows],
-                Gen.Int[900, 1000].Array[rows],
+                Gen.Int[0, 5].Array()[cols].Where(a => a.Sum() > 0).Array()[rows],
+                Gen.Int[900, 1000].Array()[rows],
                 Gen.Int.Uniform))
         .Sample((solution,
                  rowPrice,
@@ -222,9 +222,9 @@ public async Task Example10()
     {
         Gen.Int[2, 20].SelectMany(rows =>
             Gen.Select(
-                Gen.Int[1, 300].Array[rows],
-                Gen.Int[1, 100].Array[rows],
-                Gen.Int[1, 1000].Select(i => (double)i).Array[2, 10],
+                Gen.Int[1, 300].Array()[rows],
+                Gen.Int[1, 100].Array()[rows],
+                Gen.Int[1, 1000].Select(i => (double)i).Array()[2, 10],
                 Gen.Int.Uniform))
         .Sample((rowPrice, rowTotal, weight, seed) =>
         {
@@ -274,9 +274,9 @@ public async Task AllocateTest()
     {
         Gen.Int[2, 20].SelectMany(rows =>
             Gen.Select(
-                Gen.Int[1, 300].Array[rows],
-                Gen.Int[1, 100].Array[rows],
-                Gen.Int[1, 1000].Select(i => (double)i).Array[2, 10],
+                Gen.Int[1, 300].Array()[rows],
+                Gen.Int[1, 100].Array()[rows],
+                Gen.Int[1, 1000].Select(i => (double)i).Array()[2, 10],
                 Gen.Int.Uniform))
         .Sample((rowPrice, rowTotal, weight, seed) =>
         {

Tests/Allocator_Tests.cs

@@ -1,4 +1,4 @@
-namespace Tests;
+namespace Tests;
 
 using System;
 using System.Collections.Generic;
@@ -11,16 +11,16 @@
 public class Allocator_Tests
 {
     readonly static Gen<(long Quantity, double[] Weights)> genAllSigns =
-        Gen.Select(Gen.Long[-10_000, 10_000], Gen.Double[-10_000, 10_000].Array[2, 50].Where(ws => ws.Sum() > 1e-9));
+        Gen.Select(Gen.Long[-10_000, 10_000], Gen.Double[-10_000, 10_000].Array()[2, 50].Where(ws => ws.Sum() > 1e-9));
 
     readonly static Gen<(long Quantity, long[] Weights)> genAllSignsLong =
-        Gen.Select(Gen.Long[-10_000, 10_000], Gen.Long[-100_000, 100_000].Array[2, 50].Where(ws => ws.Sum() != 0));
+        Gen.Select(Gen.Long[-10_000, 10_000], Gen.Long[-100_000, 100_000].Array()[2, 50].Where(ws => ws.Sum() != 0));
 
     readonly static Gen<(long Quantity, double[] Weights)> genPositive =
-        Gen.Select(Gen.Long[1, 10_000], Gen.Double[0, 10_000].Array[2, 50].Where(ws => Math.Abs(ws.Sum()) > 1e-9));
+        Gen.Select(Gen.Long[1, 10_000], Gen.Double[0, 10_000].Array()[2, 50].Where(ws => Math.Abs(ws.Sum()) > 1e-9));
 
     readonly static Gen<(long Quantity, long[] Weights)> genPositiveLong =
-        Gen.Select(Gen.Long[1, 10_000], Gen.Long[0, 100_000].Array[2, 50].Where(ws => ws.Sum() != 0));
+        Gen.Select(Gen.Long[1, 10_000], Gen.Long[0, 100_000].Array()[2, 50].Where(ws => ws.Sum() != 0));
 
     static bool TotalCorrectly<W>(long quantity, W[] weights, Func<long, W[], long[]> allocator)
         => allocator(quantity, weights).Sum() == quantity;
@@ -276,7 +276,7 @@ public void Allocate_HasSmallestAllocationError()
             var genInt = Gen.Int[0, i - 1];
             return Gen.Select(genInt, genInt)
                 .Where((i, j) => i != j)
-                .HashSet[1, i];
+                .HashSet()[1, i];
         }
         genAllSigns.Where((_, ws) => ws.Length >= 2)
         .SelectMany((quantity, weights) => GenChanges(weights.Length).Select(i => (quantity, weights, i)))
@@ -318,7 +318,7 @@ public void Allocate_Long_HasSmallestAllocationError()
             var genInt = Gen.Int[0, i - 1];
             return Gen.Select(genInt, genInt)
                 .Where((i, j) => i != j)
-                .HashSet[1, i];
+                .HashSet()[1, i];
         }
         genAllSignsLong.Where((_, ws) => ws.Length >= 2)
         .SelectMany((quantity, weights) => GenChanges(weights.Length).Select(i => (quantity, weights, i)))

Tests/CacheTests.cs

@@ -1,4 +1,4 @@
-namespace Tests;
+namespace Tests;
 
 using CsCheck;
 using System.Collections.Concurrent;
@@ -11,7 +11,7 @@ public void Cache_GetOrAdd_ModelBased()
         static void CacheTryAdd(Cache<int, byte> cache, int key, byte value)
             => cache.GetOrAdd(key, _ => Task.FromResult(value)).AsTask().GetAwaiter().GetResult();
 
-        Gen.Select(Gen.Int, Gen.Byte).Array
+        Gen.Select(Gen.Int, Gen.Byte).Array()
         .Select(kvs =>
         {
             var cache = new Cache<int, byte>();
@@ -33,7 +33,7 @@ static void CacheTryAdd(Cache<int, byte> cache, int key, byte value)
     [Test]
     public async Task Cache_GetOrAdd_StampedeFree()
     {
-        await Gen.Int.HashSet[1, 10].SampleAsync(async ks =>
+        await Gen.Int.HashSet()[1, 10].SampleAsync(async ks =>
         {
             var alreadyRun = 0;
             var ks0 = ks.First();
@@ -147,7 +147,7 @@ async Task<int> Factory(int _)
     [Test]
     public async Task Cache_Update_StampedeFree()
     {
-        await Gen.Int.HashSet[1, 10].SampleAsync(async ks =>
+        await Gen.Int.HashSet()[1, 10].SampleAsync(async ks =>
         {
             var alreadyRun = 0;
             var callCount = 0;