Move features to the separated classes

Author: sakno

src/DotNext/Buffers/SpanOwner.cs

@@ -38,7 +38,7 @@ public ref struct SpanOwner<T>
     /// </remarks>
     [EditorBrowsable(EditorBrowsableState.Never)]
     [CLSCompliant(false)]
-    public static int StackallocThreshold { get; } = 1 + (LibrarySettings.StackallocThreshold / Unsafe.SizeOf<T>());
+    public static int StackallocThreshold { get; } = 1 + Features.StackallocThreshold / Unsafe.SizeOf<T>();
 
     private readonly object? owner;
     private readonly Span<T> memory;
@@ -137,7 +137,7 @@ static unsafe Span<T> Allocate(int length)
     private static bool IsNaturalAlignment => Intrinsics.AlignOf<T>() <= nuint.Size;
 
     private static bool UseNativeAllocation
-        => LibrarySettings.UseNativeAllocation && !RuntimeHelpers.IsReferenceOrContainsReferences<T>();
+        => Features.UseNativeAllocation && !RuntimeHelpers.IsReferenceOrContainsReferences<T>();
 
     /// <summary>
     /// Gets the rented memory.
@@ -216,4 +216,31 @@ public void Dispose()
 
         this = default;
     }
+}
+
+file static class Features
+{
+    private const string UseNativeAllocationFeature = "DotNext.Buffers.NativeAllocation";
+
+    // TODO: [FeatureSwitchDefinition(EnableNativeAllocationFeature)]
+    internal static bool UseNativeAllocation
+        => LibraryFeature.IsSupported(UseNativeAllocationFeature);
+    
+    internal static int StackallocThreshold
+    {
+        get
+        {
+            const string environmentVariableName = "DOTNEXT_STACK_ALLOC_THRESHOLD";
+            const string configurationParameterName = "DotNext.Buffers.StackAllocThreshold";
+            const int defaultValue = 511;
+            const int minimumValue = 14;
+
+            if (AppContext.GetData(configurationParameterName) is not int result)
+            {
+                int.TryParse(Environment.GetEnvironmentVariable(environmentVariableName), out result);
+            }
+
+            return result > minimumValue ? result : defaultValue;
+        }
+    }
 }

src/DotNext/LibraryFeature.cs

@@ -0,0 +1,9 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace DotNext;
+
+internal static class LibraryFeature
+{
+    internal static bool IsSupported([ConstantExpected] string featureName)
+        => !AppContext.TryGetSwitch(featureName, out var result) || result;
+}

src/DotNext/LibrarySettings.cs

@@ -139,7 +139,7 @@ ref MemoryMarshal.GetReference(allowedInput),
             new CachedRandomNumberGenerator<TRandom>(random, randomVectorBuffer.Span).Randomize(allowedInput, buffer);
         }
 
-        if (LibrarySettings.UseRandomStringInternalBufferCleanup)
+        if (Features.UseRandomStringInternalBufferCleanup)
             randomVectorBuffer.Span.Clear();
 
         static void FastPath(ref uint randomVectorPtr, ref T inputPtr, uint moduloOperand, Span<T> output)
@@ -468,4 +468,13 @@ public static Optional<T> Peek<T>(this Random random, ReadOnlySpan<T> span)
             _ => span[random.Next(length)],
         };
     }
+}
+
+file static class Features
+{
+    private const string UseRandomStringInternalBufferCleanupFeature = "DotNext.Security.RandomStringInternalBufferCleanup";
+    
+    // TODO: [FeatureSwitchDefinition(UseRandomStringInternalBufferCleanupFeature)]
+    internal static bool UseRandomStringInternalBufferCleanup
+        => LibraryFeature.IsSupported(UseRandomStringInternalBufferCleanupFeature);
 }