C# - StyleCop - SA1121: UseBuiltInTypeAlias - Readability Rules

Question

Not found it in StyleCop Help Manual, on SO and Google so here it is ;)

During StyleCop use I have a warning:

SA1121 - UseBuiltInTypeAlias - Readability Rules

The code uses one of the basic C# types, but does not use the built-in alias for the type.

Rather than using the type name or the fully-qualified type name, the built-in aliases for these types should always be used: bool, byte, char, decimal, double, short, int, long, object, sbyte, float, string, ushort, uint, ulong.

so String.Empty is wrong (depend on above rules) and string.Empty is good.

Why using built-in aliases is better? Can String. Int32, Int64 (etc.) complicate something in the code on special scenarios?

Answer 1

Just to clarify: not everyone agrees with the authors of StyleCop. Win32 and .NET guru Jeffrey Richter writes in his excellent book CLR via C#:

The C# language specification states, “As a matter of style, use of the keyword is favored over use of the complete system type name.” I disagree with the language specification; I prefer to use the FCL type names and completely avoid the primitive type names. In fact, I wish that compilers didn’t even offer the primitive type names and forced developers to use the FCL type names instead. Here are my reasons:

• I’ve seen a number of developers confused, not knowing whether to use string or String in their code. Because in C# string (a keyword) maps exactly to System.String (an FCL type), there is no difference and either can be used. Similarly, I’ve heard some developers say that int represents a 32-bit integer when the application is running on a 32-bit OS and that it represents a 64-bit integer when the application is running on a 64-bit OS. This statement is absolutely false: in C#, an int always maps to System.Int32, and therefore it represents a 32-bit integer regardless of the OS the code is running on. If programmers would use Int32 in their code, then this potential confusion is also eliminated.

• In C#, long maps to System.Int64, but in a different programming language, long could map to an Int16 or Int32. In fact, C++/CLI does treat long as an Int32. Someone reading source code in one language could easily misinterpret the code’s intention if he or she were used to programming in a different programming language. In fact, most languages won’t even treat long as a keyword and won’t compile code that uses it.

• The FCL has many methods that have type names as part of their method names. For example, the BinaryReader type offers methods such as ReadBoolean, ReadInt32, ReadSingle, and so on, and the System.Convert type offers methods such as ToBoolean, ToInt32, ToSingle, and so on. Although it’s legal to write the following code, the line with float feels very unnatural to me, and it’s not obvious that the line is correct:

  BinaryReader br = new BinaryReader(...); float val = br.ReadSingle(); // OK, but feels unnatural Single val = br.ReadSingle(); // OK and feels good 

• Many programmers that use C# exclusively tend to forget that other programming languages can be used against the CLR, and because of this, C#-isms creep into the class library code. For example, Microsoft’s FCL is almost exclusively written in C# and developers on the FCL team have now introduced methods into the library such as Array’s GetLongLength, which returns an Int64 value that is a long in C# but not in other languages (like C++/CLI). Another example is System.Linq.Enumerable’s LongCount method.

Answer 2

It would only really complicate the code if you had your own String, Int32 etc types which might end up being used instead of System.* - and please don't do that!

Ultimately it's a personal preference. I use the aliases everywhere, but I know some people (e.g. Jeffrey Richter) advise never using them. It's probably a good idea to be consistent, that's all. If you don't like that StyleCop rule, disable it.

Note that names of methods etc should use the framework name rather than the alias, so as to be language-neutral. This isn't so important for private / internal members, but you might as well have the same rules for private methods as public ones.