59 lines
1.6 KiB
Plaintext
59 lines
1.6 KiB
Plaintext
In C#, delegates can be added together to chain their execution, and subtracted to remove their execution from the chain.
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Subtracting a chain of delegates from another one might yield unexpected results as shown hereunder - and is likely to be a bug.
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== Noncompliant Code Example
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[source,csharp]
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----
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MyDelegate first, second, third, fourth;
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first = () => Console.Write("1");
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second = () => Console.Write("2");
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third = () => Console.Write("3");
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fourth = () => Console.Write("4");
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MyDelegate chain1234 = first + second + third + fourth; // Compliant - chain sequence = "1234"
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MyDelegate chain12 = chain1234 - third - fourth; // Compliant - chain sequence = "12"
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MyDelegate chain14 = first + fourth; // creates a new MyDelegate instance which is a list under the covers
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MyDelegate chain23 = chain1234 - chain14; // Noncompliant; (first + fourth) doesn't exist in chain1234
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// The chain sequence of "chain23" will be "1234" instead of "23"!
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// Indeed, the sequence "1234" does not contain the subsequence "14", so nothing is subtracted
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// (but note that "1234" contains both the "1" and "4" subsequences)
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chain23 = chain1234 - (first + fourth); // Noncompliant
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chain23(); // will print "1234"!
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----
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== Compliant Solution
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[source,csharp]
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----
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MyDelegate chain23 = chain1234 - first - fourth; // Compliant - "1" is first removed, followed by "4"
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chain23(); // will print "23"
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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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include::message.adoc[]
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'''
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== Comments And Links
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(visible only on this page)
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include::comments-and-links.adoc[]
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endif::env-github,rspecator-view[]
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