[Foundation] Fix nullability in NSMutableDictionary<TKey, TValue>. #24458
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This is file 40 of 47 files with nullability disabled in Foundation.
* Enabled nullable reference types.
* Removed four SupportedOSPlatform attributes without version numbers.
* Replaced 'To be added.' XML comments with proper documentation.
* Added XML documentation for all public and protected members.
* Used ArgumentNullException.ThrowIfNull for parameter validation.
* Fixed XML comment formatting and added see cref attributes.
* Made ObjectForKey return nullable TValue? since keys may not exist.
* Made TryGetValue parameter nullable with NotNullWhen(true) attribute.
* Kept IDictionary interface implementations non-nullable per .NET contract.
* Used KeyNotFoundException when indexer accesses missing keys.
* Fixed IEnumerator implementations to skip null values in enumeration.
* Changed empty array initialization from 'new TValue[]{}' to '[]'.
* Remove some dead code.
* Add a few more tests.
Contributes towards #17285.
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Pull request overview
This PR enables nullable reference types for NSMutableDictionary<TKey, TValue>, which is file 40 of 47 in the Foundation nullability migration effort. The changes improve type safety by making nullability explicit in method signatures, particularly for methods that can return null for missing keys like ObjectForKey. The PR also improves the indexer behavior to throw KeyNotFoundException for missing keys (aligning with .NET conventions), replaces placeholder XML documentation with comprehensive summaries, and modernizes parameter validation using ArgumentNullException.ThrowIfNull.
Key changes:
- Made
ObjectForKeyreturnTValue?(nullable) since keys may not exist in the dictionary - Changed public indexer getter to throw
KeyNotFoundExceptionfor missing keys instead of returning null - Added comprehensive XML documentation for all public members
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| src/Foundation/NSMutableDictionary_2.cs | Enabled nullable reference types, updated method signatures for nullability, replaced placeholder XML docs with comprehensive documentation, modernized parameter validation, changed indexer to throw KeyNotFoundException for missing keys |
| tests/monotouch-test/Foundation/NSMutableDictionary2Test.cs | Added comprehensive tests for missing key access behavior, testing ObjectForKey, TryGetValue, ContainsKey, indexer, and IDictionary interface behavior |
| tests/cecil-tests/Documentation.KnownFailures.txt | Removed entries for methods that now have proper XML documentation |
| { | ||
| return TryGetValue (key, out value); | ||
| var result = TryGetValue (key, out var nullableValue); | ||
| value = nullableValue!; |
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The coding guidelines state "Don't ever use ! to handle null!" The null-forgiving operator should be avoided. Instead, this could be rewritten to avoid the null-forgiving operator, for example by using a conditional assignment or restructuring the code.
| // But accessing via IDictionary interface should return null | ||
| IDictionary<NSString, NSDate> idict = dict; | ||
| Assert.IsNull (idict [keyMissing], "missing key via interface"); |
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The test expects the IDictionary indexer to return null for missing keys, but the implementation at line 380 calls the public indexer which throws KeyNotFoundException. According to the .NET IDictionary interface contract, the indexer getter should throw KeyNotFoundException when the key is not found, not return null. Either this test assertion is incorrect, or the IDictionary indexer implementation should be changed to return ObjectForKey directly to maintain backwards compatibility (though that would violate .NET conventions).
| // But IDictionary indexer should return null | ||
| IDictionary<NSString, NSDate> idict = dict; | ||
| Assert.IsNull (idict [keyMissing], "IDictionary indexer missing"); |
There was a problem hiding this comment.
The test expects the IDictionary indexer to return null for missing keys, but the implementation at line 380 calls the public indexer which throws KeyNotFoundException. According to the .NET IDictionary interface contract, the indexer getter should throw KeyNotFoundException when the key is not found, not return null. Either this test assertion is incorrect, or the IDictionary indexer implementation should be changed to return ObjectForKey directly to maintain backwards compatibility (though that would violate .NET conventions).
| IDictionary<NSString, NSDate> idict = dict; | ||
| Assert.IsNull (idict [keyMissing], "IDictionary indexer"); |
There was a problem hiding this comment.
The test expects the IDictionary indexer to return null for missing keys, but the implementation at line 380 calls the public indexer which throws KeyNotFoundException. According to the .NET IDictionary interface contract, the indexer getter should throw KeyNotFoundException when the key is not found, not return null. Either this test assertion is incorrect, or the IDictionary indexer implementation should be changed to return ObjectForKey directly to maintain backwards compatibility (though that would violate .NET conventions).
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This is file 40 of 47 files with nullability disabled in Foundation.
Contributes towards #17285.