Fixed bug that would cause a struct to not match and throw a runtime error. #895
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…time error. When a struct had an empty constructor that modified a field/property to a non-default value. The matcher would fail and throw a runtime error. This bug fix attempts to fix that issue by essentially zero initializing the struct the same way that default(T) does through the use of a runtime helper method. Simply, we replace Activator.CreateInstance with GetUninitializedObject. The idea came from this post https://stackoverflow.com/questions/1005336/c-sharp-using-reflection-to-create-a-struct Which contains and deprecated method as of .NET8. Microsoft has a recommended fix for that here. https://learn.microsoft.com/en-us/dotnet/fundamentals/syslib-diagnostics/syslib0050
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Thanks for the pull request! Could you please add some unit tests? |
- Added test method `Any_on_struct_with_default_constructor_should_work` to ensure method calls with struct arguments do not throw exceptions. - Introduced `StructWithDefaultConstructor` struct: - Contains a property `Value`. - Has a default constructor initializing `Value` to 42. - Created `IWithStructWithDefaultConstructor` interface: - Declares `MethodWithStruct` that accepts `StructWithDefaultConstructor` as an argument.
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I added a simple test that does fail on the main branch. Not sure there is a whole lot to test here. I did ensure that all tests pass, especially ones that take in nullable primitive types like |
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Is there anything still blocking this from being merged? |
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I fixed the format issue. |
Only a review I guess 😅 |
| @@ -46,6 +46,15 @@ private object DefaultInstanceOfValueType(Type returnType) | |||
| return BoxedDouble; | |||
| } | |||
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| return Activator.CreateInstance(returnType)!; | |||
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I'm doubting if we should use Activator.CreateInstance(returnType)!; for non-stucts, to keep things 100% the same for the previous cases.
Although all tests works, so not sure.
@nsubstitute/core-team any opinion on this?
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Pull Request Overview
This PR fixes a runtime error that occurred when using NSubstitute's Arg.Any<T>() matcher with structs that have non-default constructors. The issue arose because Activator.CreateInstance would invoke the constructor, causing the matcher to fail when comparing against the modified struct values.
- Replaces
Activator.CreateInstancewithGetUninitializedObjectto create zero-initialized structs - Adds special handling for
Nullable<T>types to return null - Implements conditional compilation for .NET 5+ vs older frameworks
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| src/NSubstitute/Core/DefaultForType.cs | Updates struct instantiation logic to use GetUninitializedObject instead of Activator.CreateInstance |
| tests/NSubstitute.Acceptance.Specs/ArgumentMatching.cs | Adds regression test for struct with default constructor scenario |
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When a struct had an empty constructor that modified a field/property to a non-default value. The matcher would fail and throw a runtime error. This bug fix attempts to fix that issue by essentially zero initializing the struct the same way that
default(T)does through the use of a runtime helper method. Simply, we replaceActivator.CreateInstancewithGetUninitializedObject.The idea came from this post
Which contains and deprecated method as of .NET8. Microsoft has a recommended fix for that here.
This resolves the issue in #766