Summary

Every WikiTalk object is of a particular type. That type governs what the object can do.

Overview

This server's WikiTalk has 46 different types built in. These include simple types like String and Number, fancy types like DateTime and TimeSpan, and wiki specific types like Topic and TopicChange. Each server installation can add to the list of types, but is not possible to add new types from WikiTalk programs. See WikiTalkTypeHierarchy for the complete list of types.

Each type defines a set of properties and methods collectively called members. See WikiTalkMembers.

It is possible to ask an object what type it is using the Type property. For example:

 DateTime.Now.Type

will answer back the type of the Now DateTime object (obviously a DateTime). For another example:

 "hello world".Length.Type

will answer back the type of the length of the string "hello world". The length is 11 and the type of 11 is Integer.

What good is a type, anyway?

Types are typically used to perform Reflection operations (see WikiTalkReflection). For example, once you have the DateTime type, you can ask it questions -- e.g., what properties and methods to you have. In fact that is exactly how the list above is generated. Specifically, a Type has a property called Members which answers a collection of WikiTalkMember objects, each of which define a property or method of the associated type.

Getting your hands on a Type

There are two way to get to a type. The first is by asking an object for its type:

 DateTime.Now.Type
 100.Type
 topic.Type

These will all answer back an appropriate Type object.

All of the WikiTalk types also are simply accessible by name in WikiTalk:

 DateTime.Now

In the above expression, DateTime is the DateTime type.

The other useful thing about Types

As you can see in the above example, Types have not only general things you can ask them that apply to all types (e.g., what are the properties that instances of you have?). Many Types also have specific properties or methods that are only applicable to that type. Now is an example of such a property; it only makes sense for DateTime.

MetaTypes

If every object has a type, what happens when you ask a Type for its Type?

Well, it turns out you get another kind of object called a MetaType. Each Type has a corresponding MetaType. This MetaType object can answer back information about the Type (as opposed to the Type which generally answers back information about its instances).

This can be pretty confusing, so I'll give an example:

If I ask a DateTime for its type, I'll get the Type DataTime.

 topic.LastModified.Type

topic.LastModified answers back the time when the current topic was last modified. The type of object here is a DateTime.

If I ask that type for its Members:

 topic.LastModified.Type.Members.Collect 
   { e | ["        *", e.Signature, Newline] }

I will get a list of properties and methods that make sense for a DateTime:

String ToShortDateString
DateTime Subtract(Object span)
Integer Second
String ToShortTimeString
Integer Month
String ToLongDateString
DateTime AddDays(Integer delta)
Object Equals(Object obj)
Integer Hour
Integer Minute
Integer Day
DateTime AddSeconds(Integer delta)
DateTime AddMinutes(Integer delta)
Object SpanBetween(DateTime aDateTime)
DateTime AddHours(Integer delta)
Integer DayOfYear
Object TimeOfDay
DateTime AddMonths(Integer delta)
Integer Year
DateTime AddYears(Integer delta)
Integer Millisecond
DateTime ToUniversalTime
DateTime ToLocalTime
String ToLongTimeString
DateTime Date
DateTime AddMilliseconds(Integer delta)
String DayOfWeek
DateTime Add(Object span)

So, when I say DateTime.Now, what is Now a property of? It's clearly not a property of DateTime (see the above list ). Instead, it is part of the DateType MetaType (designated DateTimeType). if I ask this object (DateTimeType) for its members, I'll get something very different:

 topic.LastModified.Type.Type.Members.Collect 
   { e | ["        *", e.Signature, Newline]}

specifically:

DateTime Now
DateTime Instance(Integer year, Integer month, Integer day, Integer hour {optional}, Integer minute {optional}, Integer second {optional}, Integer millisecond {optional})
DateTime Today
DateTime MaxValue
Integer DaysInMonth(Integer year, Integer month)
DateTime InstanceFromString(String s)
DateTime UtcNow
Object IsLeapYear(Integer year)
Integer WeeksInMonth(Integer year, Integer month, Integer firstDayOfWeek)
DateTime MinValue

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