3

In C#, when I enclose an int value in brackets and type the dot, I get a list of functions that can be performed on that int value

string a = (12).ToString();

My question is, how can we define a custom function like that? For example I want to define a function toDateTime which can work like this

DateTime dt = ("12/12/12").toDateTime();

I fully understand that this can be done by the normal way also

DateTime dt = toDateTime("12/12/12");

I am just curious about how it is done by the other way.

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2
  • Maybe through Extension Methods? Commented Mar 5, 2013 at 8:42
  • 1
    Side note: There is nothing special about () - the reason you need to use braces around int constants to get intellisence is VS treats "12." as beginning of float number, unlike in all other types (i.e. string : "aaa". shows intelisence for string). Commented Mar 5, 2013 at 8:45

4 Answers 4

Reset to default
7

You can create an Extension Method

Maybe like this:

public static class MyExtensions
{
     public static DateTime ToDateTime(this String str)
     {
         // return something
     }
}
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6 Comments

@Steve: sorry, I fix the parameter type to string instead DateTime
Good, but why don't add the actual code that translates that string in a datetime? That will complete the answer
@Steve I don't think this is necessary, as it's outside the scope of the actual question, imho
@Nolonar, we have different opinions on what is useful for the site visitors.
@Steve No, we simply have different logic and thought processes. I believe Ambar's question is hypothetical, there is no evidence that he really wants to convert a string to a DateTime, as seen in his question's title (int).function(). Also, I doubt that anyone looking for How to convert string to DateTime will ever come to this question. There are enough links explaining the specifics already. Also, you are welcome to edit the answer to make it more clear or useful or complete. I simply believe it's not necessary (but it would be useful indeed)
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6

What you are describing are extension methods.

These are static classes and methods that the IDE (Visual Studio) makes look like they are part of the extended type.

Note that there is no need to enclose the type in parenthesis:

string a = 12.ToString(); // not an extension method - it is defined on Object
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3 Comments

+1. You need braces for intellisence to pick up dot in case of integer literals :)
@AlexeiLevenkov - Ctrl + Space is normally enough.
Yes, but there is no magically appearing list without braces.
4

You can not: these functions on primitive types, and functions like ToString, which is defined in Object, are provided by the framework. However, you can obtain (more or less) the same result by using extension methods instead.

Extension methods are static functions in static classes that the IDE (VS) and the compiler treat as member functions of the class defined by the first parameter (marked with this). They are not actually the same as adding member functions: their resolution and precedence are different.

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1 Comment

Upvoted for clarity, ToString() is a member of Object and not a extension method
2

You can use extension method

public static DateTime ToDateTime(this string datestring)
{
    return DateTime.Parse(datestring);
}

Extension methods can be packed within a static class

Example : 

static class Program
{
    public static DateTime ToDateTime(this string datestring)
    {
        return DateTime.Parse(datestring);
    }
    static void Main(string[] args)
    {
        DateTime date = "12/12/12".ToDateTime();

    }
}
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