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Change ParameterDefaultValue to use GetUninitializedObject instead of Activator.CreateInstance #47722

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merged 2 commits into from
Feb 5, 2021
Merged

Change ParameterDefaultValue to use GetUninitializedObject instead of Activator.CreateInstance #47722

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dfdf999
Change ParameterDefaultValue to use GetUninitializedObject instead of…
eerhardt Feb 1, 2021
69256fa
Add test for struct with default constructor
eerhardt Feb 1, 2021
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28 changes: 19 additions & 9 deletions src/libraries/Common/src/Extensions/ParameterDefaultValue/ParameterDefaultValue.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,12 +7,16 @@
using System.Diagnostics.CodeAnalysis;
using System.Reflection;

#if NETFRAMEWORK || NETSTANDARD2_0
using System.Runtime.Serialization;
#else
using System.Runtime.CompilerServices;
#endif

namespace Microsoft.Extensions.Internal
{
internal class ParameterDefaultValue
{
private static readonly Type _nullable = typeof(Nullable<>);

public static bool TryGetDefaultValue(ParameterInfo parameter, out object? defaultValue)
{
bool hasDefaultValue;
Expand All @@ -39,21 +43,27 @@ public static bool TryGetDefaultValue(ParameterInfo parameter, out object? defau
defaultValue = parameter.DefaultValue;
}

bool isNullableParameterType = parameter.ParameterType.IsGenericType &&
parameter.ParameterType.GetGenericTypeDefinition() == typeof(Nullable<>);

// Workaround for https://github.com/dotnet/runtime/issues/18599
if (defaultValue == null && parameter.ParameterType.IsValueType)
if (defaultValue == null && parameter.ParameterType.IsValueType
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&& !isNullableParameterType) // Nullable types should be left null
{
defaultValue = CreateValueType(parameter.ParameterType);
}

[UnconditionalSuppressMessage("ReflectionAnalysis", "IL2067:UnrecognizedReflectionPattern",
Justification = "CreateInstance is only called on a ValueType, which will always have a default constructor.")]
static object? CreateValueType(Type t) => Activator.CreateInstance(t);
Justification = "CreateValueType is only called on a ValueType. You can always create an instance of a ValueType.")]
static object? CreateValueType(Type t) =>
#if NETFRAMEWORK || NETSTANDARD2_0
FormatterServices.GetUninitializedObject(t);
#else
RuntimeHelpers.GetUninitializedObject(t);
#endif

// Handle nullable enums
if (defaultValue != null &&
parameter.ParameterType.IsGenericType &&
parameter.ParameterType.GetGenericTypeDefinition() == _nullable
)
if (defaultValue != null && isNullableParameterType)
{
Type? underlyingType = Nullable.GetUnderlyingType(parameter.ParameterType);
if (underlyingType != null && underlyingType.IsEnum)
Expand Down