C# – TKey and TValue in a generic dictionary

c++generics

The names TKey and TValue in a dictionary are confusing me. Are they named with that convention for a reason or could they have named it anything?

i.e. if I create a generic, do I have to use some sort of naming convention also?

Best Solution

It is convention to use T for generic types (comparable with "templates" in C++ etc).

If there is a single type (List<T>) then just T is fine (there is nothing more to explain); but if there are multiple generic types, the T prefixes the purpose. Hence TKey is the generic type of the "key", and TValue of the value. If helps in this case if you know that a dictionary maps keys to values!

The intellisense will usually tell you what each type-argument means; for example with Func<T1,T2,TResult>:

T1: The type of the first parameter of the method that this delegate encapsulates.
T2: The type of the second parameter of the method that this delegate encapsulates.
TResult: The type of the return value of the method that this delegate encapsulates.

(taken from the type's comment data)

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C# – How to sort a dictionary by value

Use LINQ:

Dictionary<string, int> myDict = new Dictionary<string, int>();
myDict.Add("one", 1);
myDict.Add("four", 4);
myDict.Add("two", 2);
myDict.Add("three", 3);

var sortedDict = from entry in myDict orderby entry.Value ascending select entry;

This would also allow for great flexibility in that you can select the top 10, 20 10%, etc. Or if you are using your word frequency index for type-ahead, you could also include StartsWith clause as well.

C# – the difference between String and string in C#

string is an alias in C# for System.String.
So technically, there is no difference. It's like int vs. System.Int32.

As far as guidelines, it's generally recommended to use string any time you're referring to an object.

e.g.

string place = "world";

Likewise, I think it's generally recommended to use String if you need to refer specifically to the class.

e.g.

string greet = String.Format("Hello {0}!", place);

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

Best Solution

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C# – How to sort a dictionary by value

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

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