Stabilize span normalization in expression evaluation

Author: yevhen

src/SharpAssert.Runtime/Features/Shared/ExpressionValueEvaluator.cs

@@ -9,7 +9,7 @@ namespace SharpAssert.Features.Shared;
 
 static class ExpressionValueEvaluator
 {
-    static readonly MethodInfo? ToArrayMethod = ResolveToArrayMethod();
+    static readonly MethodInfo SpanToArrayMethod = typeof(ExpressionValueEvaluator).GetMethod(nameof(SpanToArray), BindingFlags.NonPublic | BindingFlags.Static)!;
     static readonly Func<object> NullEvaluator = () => null!;
 
     public static object? Evaluate(Expression expression) => Compile(expression)();
@@ -30,31 +30,6 @@ public static Func<object> Compile(Expression expression)
         return () => new EvaluationUnavailable("Evaluation failed");
     }
 
-    static MethodInfo? ResolveToArrayMethod()
-    {
-        foreach (var method in typeof(MemoryExtensions).GetMethods(BindingFlags.Public | BindingFlags.Static))
-        {
-            if (method.Name != "ToArray" || !method.IsGenericMethodDefinition)
-                continue;
-
-            var parameters = method.GetParameters();
-            if (parameters.Length != 1)
-                continue;
-
-            if (IsReadOnlySpan(parameters[0].ParameterType))
-                return method;
-        }
-
-        return null;
-    }
-
-    static bool IsReadOnlySpan(Type type)
-    {
-        return type.IsByRefLike &&
-               type.IsGenericType &&
-               type.GetGenericTypeDefinition() == typeof(ReadOnlySpan<>);
-    }
-
     static Expression Normalize(Expression expression)
     {
         if (!expression.Type.IsByRefLike)
@@ -70,14 +45,9 @@ static Expression Normalize(Expression expression)
             ? expression
             : Expression.Convert(expression, readOnlySpanType);
 
-        if (ToArrayMethod != null)
-        {
-            var toArray = ToArrayMethod.MakeGenericMethod(elementType);
-            var call = Expression.Call(toArray, spanExpression);
-            return Expression.Convert(call, typeof(object));
-        }
-
-        return Expression.Constant(new EvaluationUnavailable("Span conversion unavailable"), typeof(object));
+        var toArray = SpanToArrayMethod.MakeGenericMethod(elementType);
+        var call = Expression.Call(toArray, spanExpression);
+        return Expression.Convert(call, typeof(object));
     }
 
     static bool TryInterpret(Expression expression, out Func<object> result)
@@ -201,4 +171,6 @@ static bool TryEvaluateMember(MemberExpression member, out object value)
 
         static object? TargetOrNull(object? targetValue) => targetValue is EvaluationUnavailable ? null : targetValue;
     }
+
+    static T[] SpanToArray<T>(ReadOnlySpan<T> span) => span.ToArray();
 }