C# – Why implement standard exception constructors

ccoding-styleexception

From MSDN, code analysis warning CA1032:

Exception types must implement the following constructors: 
public NewException() 
public NewException(string) 
public NewException(string, Exception) 
protected or private NewException(SerializationInfo, StreamingContext)

I understand the purpose behind the serialization constructor, but is the rationale behind "requiring" the others? Why shouldn't I just define whatever constructors make sense for usage of my exception? What if I never want to throw MyException without passing in a message- why should I define a parameterless constructor? What if I want MyException to have an int property and I only want constructors that initialize that property?

Best Answer

This is a warning, not a requirement. It's basically principle of least surprise. Providing all 4 makes it easier for people used to "regular" C# exceptions to use yours. If you have a good reason to ignore the guideline, do so. But it will break certain usage scenarios, and make your class a little less intuitive.

Related Solutions

Python – How to test that a Python function throws an exception

Use TestCase.assertRaises (or TestCase.failUnlessRaises) from the unittest module, for example:

import mymod

class MyTestCase(unittest.TestCase):
    def test1(self):
        self.assertRaises(SomeCoolException, mymod.myfunc)

C# – Order of items in classes: Fields, Properties, Constructors, Methods

According to the StyleCop Rules Documentation the ordering is as follows.

Within a class, struct or interface: (SA1201 and SA1203)

Constant Fields
Fields
Constructors
Finalizers (Destructors)
Delegates
Events
Enums
Interfaces (interface implementations)
Properties
Indexers
Methods
Structs
Classes

Within each of these groups order by access: (SA1202)

public
internal
protected internal
protected
private

Within each of the access groups, order by static, then non-static: (SA1204)

static
non-static

Within each of the static/non-static groups of fields, order by readonly, then non-readonly : (SA1214 and SA1215)

readonly
non-readonly

An unrolled list is 130 lines long, so I won't unroll it here. The methods part unrolled is:

public static methods
public methods
internal static methods
internal methods
protected internal static methods
protected internal methods
protected static methods
protected methods
private static methods
private methods

The documentation notes that if the prescribed order isn't suitable - say, multiple interfaces are being implemented, and the interface methods and properties should be grouped together - then use a partial class to group the related methods and properties together.

Best Answer

Related Solutions

Python – How to test that a Python function throws an exception

C# – Order of items in classes: Fields, Properties, Constructors, Methods

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