Improve dynamic building

src/flatcollections-array/FlatArray.Tests/Internal.Helper/FlatArray/FlatArray.Verify.cs

@@ -1,4 +1,6 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using Xunit;
 
 namespace PrimeFuncPack.Core.Tests;
@@ -11,6 +13,22 @@ internal static void VerifyInnerState<T>(this FlatArray<T> actual, T[]? expected
         Assert.StrictEqual(expectedLength, actualLength);
 
         var actualItems = actual.GetFieldValue<T[]?>("items");
-        Assert.Equal(expectedItems, actualItems);
+        var effectiveItems = actualItems is null
+            ? null
+            : new ReadOnlySpan<T>(actualItems, 0, actualLength).ToArray();
+
+        Assert.Equal(expectedItems, effectiveItems);
+
+        if (actualItems is not null)
+        {
+            var effectiveRest = new ReadOnlySpan<T>(
+                actualItems,
+                actualLength,
+                actualItems.Length - effectiveItems!.Length)
+                .ToArray();
+
+            var actualRestIsDefault = effectiveRest.All(item => EqualityComparer<T>.Default.Equals(item, default));
+            Assert.True(actualRestIsDefault);
+        }
     }
 }

src/flatcollections-array/FlatArray.Tests/Tests.FlatArray.T.Builder/Builder/Builder.MoveToFlatArray.cs

@@ -30,11 +30,11 @@ public void MoveToFlatArray_SourceIsNotDefault_ExpectArrayItemsAreBuilderItems()
     {
         const int length = 3;
 
-        var sourceItems = new[] { PlusFifteenIdRefType, null, MinusFifteenIdRefType, ZeroIdRefType };
+        var sourceItems = new[] { PlusFifteenIdRefType, null, MinusFifteenIdRefType, null };
         var source = sourceItems.InitializeFlatArrayBuilder(length);
 
         var actual = source.MoveToFlatArray();
-        var expectedItems = new[] { PlusFifteenIdRefType, null, MinusFifteenIdRefType, ZeroIdRefType };
+        var expectedItems = new[] { PlusFifteenIdRefType, null, MinusFifteenIdRefType };
 
         actual.VerifyInnerState(expectedItems, length);
     }

src/flatcollections-array/FlatArray/FlatArray.T.Builder/FlatArray.Builder.TrimExcess.cs

@@ -1,6 +1,4 @@
-using System.Runtime.CompilerServices;
-
-namespace System;
+namespace System;
 
 partial struct FlatArray<T>
 {
@@ -14,7 +12,7 @@ internal void TrimExcess()
             var length = this.length;
             var items = this.items;
 
-            if (length == items.Length)
+            if (items.Length == length)
             {
                 return;
             }

src/flatcollections-array/FlatArray/FlatArray.T.JsonConverter/FlatArray.JsonConverter.Read.cs

@@ -42,12 +42,7 @@ public override FlatArray<T> Read(ref Utf8JsonReader reader, Type typeToConvert,
                 array[actualCount++] = InnerReadItem(ref reader, options);
             }
 
-            if (actualCount < array.Length)
-            {
-                InnerArrayHelper.TruncateUnchecked(ref array, actualCount);
-            }
-
-            return new(array, default);
+            return new(actualCount, array);
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]

src/flatcollections-array/FlatArray/FlatArray.T/FlatArray.TrimExcess.cs

@@ -0,0 +1,9 @@
+namespace System;
+
+partial struct FlatArray<T>
+{
+    // TODO: Add the tests and make public
+    internal FlatArray<T> TrimExcess()
+        =>
+        items is null || items.Length == length ? this : new(InnerArrayHelper.Copy(items, length), default);
+}

src/flatcollections-array/FlatArray/FlatArray.T/InnerFactory/FlatArray.InnerFactory.FromIEnumerable.cs

@@ -31,12 +31,7 @@ internal static FlatArray<T> FromIEnumerable(IEnumerable<T> source, int estimate
                 array[actualCount++] = enumerator.Current;
             }
 
-            if (actualCount < array.Length)
-            {
-                InnerArrayHelper.TruncateUnchecked(ref array, actualCount);
-            }
-
-            return new(array, default);
+            return new(actualCount, array);
         }
     }
 }

src/flatcollections-array/FlatArray/FlatArray.T/InnerFactory/FlatArray.InnerFactory.FromIReadOnlyList.cs

@@ -31,12 +31,7 @@ internal static FlatArray<T> FromIReadOnlyList(IReadOnlyList<T> source)
                 actualCount++;
             }
 
-            if (actualCount < array.Length)
-            {
-                InnerArrayHelper.TruncateUnchecked(ref array, actualCount);
-            }
-
-            return new(array, default);
+            return new(actualCount, array);
         }
     }
 }