How does a static Dictionary have cyclomatic compl

问题:

I have the following class:

public static class MyClass
{
    private static readonly Dictionary<Type, Func<string, object>> valueTypes;

    static MyClass()
    {
        var dictionary = new Dictionary<Type, Func<string, object>>();
        dictionary.Add(typeof(bool), x => bool.Parse(x));
        dictionary.Add(typeof(byte), x => byte.Parse(x));
        dictionary.Add(typeof(char), x => char.Parse(x));
        dictionary.Add(typeof(decimal), x => decimal.Parse(x));
        dictionary.Add(typeof(double), x => double.Parse(x));
        dictionary.Add(typeof(float), x => float.Parse(x));
        dictionary.Add(typeof(int), x => int.Parse(x));
        dictionary.Add(typeof(long), x => long.Parse(x));
        dictionary.Add(typeof(sbyte), x => sbyte.Parse(x));
        dictionary.Add(typeof(short), x => short.Parse(x));
        dictionary.Add(typeof(uint), x => uint.Parse(x));
        dictionary.Add(typeof(ulong), x => ulong.Parse(x));
        dictionary.Add(typeof(ushort), x => ushort.Parse(x));
        MyClass.valueTypes = dictionary;
    }
}

However, Microsoft Code Analysis flags this as having a cyclomatic complexity of 27. I do not understand why a series of Add calls with delegates results in such a high cyclomatic complexity.

What can I do to reduce the cyclomatic complexity?

回答1:

I like this definition for CC - the amount of decision logic in a source code function (See more on "Code Metrics – Cyclomatic Complexity", there is also very good example how is CC calculated).

So since each Add() has two different code paths - Add() itself and Value function, so CC+=2. Since you put Add() 13 times - CC == at least 26. And regarding MSDN minimal CC is 2 and when it increased it start increasing from 1, so you ends up with 27 :) Having an anonymous method in a dictionary value increases a complexity since potentially it may raise an exception so should be covered by a test as well.

Code Metrics Values, MSDN:

Cyclomatic Complexity – Measures the structural complexity of the code. It is created by calculating the number of different code paths in the flow of the program. A program that has complex control flow will require more tests to achieve good code coverage and will be less maintainable.

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Just of interest check what are CC for these examples:

private static readonly Dictionary<Type, Func<string, object>> valueTypes
static MyClass()     
{         
    var dictionary = new Dictionary<Type, Func<string, object>>();         
    dictionary.Add(typeof(bool), x => bool.Parse(x)); 
}


static MyClass()     
{         
    var dictionary = new Dictionary<Type, Func<string, object>>();         
    Func<string, object> func = (x) => bool.Parse(x)
    dictionary.Add(typeof(bool), func); 
}

static MyClass()     
{         
    var dictionary = new Dictionary<Type, Func<string, object>>();         
    dictionary.Add(typeof(bool), null); 
}