69 lines
1.6 KiB
Plaintext
69 lines
1.6 KiB
Plaintext
== Why is this an issue?
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`GetHashCode` is used to file an object in a `Dictionary` or `Hashtable`. If `GetHashCode` uses non-`readonly` fields and those fields change after the object is stored, the object immediately becomes mis-filed in the `Hashtable`. Any subsequent test to see if the object is in the `Hashtable` will return a false negative.
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=== Exceptions
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This rule does not raise if the type implementing `GetHashCode` is a value type, for example a `struct` or a `record struct`, since when a value type is stored in a `Dictionary` or `Hashtable`, a copy of the value is stored, not a reference to the value.
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== How to fix it
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=== Code examples
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==== Noncompliant code example
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[source,csharp,diff-id=1,diff-type=noncompliant]
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----
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public class Person
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{
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public int age;
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public string name;
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public override int GetHashCode()
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{
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int hash = 12;
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hash += this.age.GetHashCode(); // Noncompliant
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hash += this.name.GetHashCode(); // Noncompliant
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return hash;
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}
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----
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==== Compliant solution
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[source,csharp,diff-id=1,diff-type=compliant]
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----
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public class Person
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{
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public readonly DateTime birthday;
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public string name;
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public override int GetHashCode()
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{
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int hash = 12;
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hash += this.birthday.GetHashCode();
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return hash;
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}
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----
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Refactor 'GetHashCode' to not reference mutable fields.
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=== Highlighting
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* primary: method name
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* secondary: uses of mutable fields
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** message: Remove this use of "xxx" or make it "readonly".
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endif::env-github,rspecator-view[]
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