95 lines
2.0 KiB
Plaintext
95 lines
2.0 KiB
Plaintext
== Why is this an issue?
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https://en.wikipedia.org/wiki/Recursion[Recursion] is a technique used to define a problem in terms of the problem itself, usually in terms of a simpler version of the problem itself.
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For example, the implementation of the generator for the n-th value of the https://en.wikipedia.org/wiki/Fibonacci_sequence[Fibonacci sequence] comes naturally from its mathematical definition, when recursion is used:
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[source,csharp]
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----
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int NthFibonacciNumber(int n)
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{
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if (n <= 1)
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{
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return 1;
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}
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else
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{
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return NthFibonacciNumber(n - 1) + NthFibonacciNumber(n - 2);
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}
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}
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----
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As opposed to:
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[source,csharp]
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----
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int NthFibonacciNumber(int n)
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{
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int previous = 0;
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int last = 1;
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for (var i = 0; i < n; i++)
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{
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(previous, last) = (last, last + previous);
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}
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return last;
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}
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----
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Use of recursion is acceptable in methods, like the one above, where you can break out of it.
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[source,csharp]
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----
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int NthFibonacciNumber(int n)
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{
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if (n <= 1)
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{
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return 1; // Base case: stop the recursion
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}
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// ...
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}
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----
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It is also acceptable and makes sense in some type definitions:
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[source,csharp]
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----
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class Box : IComparable<Box>
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{
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public int CompareTo(Box? other)
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{
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// Compare the two Box instances...
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}
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}
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----
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With types, some invalid recursive definitions are caught by the compiler:
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[source,csharp]
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----
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class C2<T> : C2<T> // Error CS0146: Circular base type dependency
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{
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}
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class C2<T> : C2<C2<T>> // Error CS0146: Circular base type dependency
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{
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}
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----
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In more complex scenarios, however, the code will compile but execution will result in a https://learn.microsoft.com/en-us/dotnet/api/system.typeloadexception[TypeLoadException] if you try to instantiate the class.
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[source,csharp]
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----
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class C1<T>
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{
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}
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class C2<T> : C1<C2<C2<T>>> // Noncompliant
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{
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}
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var c2 = new C2<int>(); // This would result into a TypeLoadException
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----
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include::../resources.adoc[]
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include::../rspecator.adoc[]
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