Understanding Anonymous Types
Anonymous types defined with var are not VB variants. The var keyword signals
the compiler to emit a strong type based on the value of the operator on the
right side. Anonymous types can be used to initialize simple types like
integers and strings but detract modestly from clarity and add little value.
Where var adds punch is by initializing composite types on the fly, such as
those returned from LINQ queries. When such an anonymous type is defined, the
compiler emits an immutable—read-only properties—class referred to as a
projection.
Anonymous types support IntelliSense, but the class should not be referred to in
code, just the members.
The following list includes some basic rules for using anonymous types:
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Anonymous types must always have an initial assignment and it can’t be null
because the type is inferred and fixed to the initializer.
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Anonymous types can be used with simple or complex types but add little value
to simple type definitions.
-
Composite anonymous types require member declarators; for example, var joe =
new {Name=”Joe” [, declaratory=value, ...]}. (In the example, Name is the
member declaratory.)
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Anonymous types support IntelliSense.
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Anonymous types cannot be used for a class field.
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Anonymous types can be used as initializers in for loops.
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The new keyword can be used and has to be used for array initializers.
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Anonymous types can be used with arrays.
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Anonymous types are all derived from the Object type.
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Anonymous types can be returned from methods but must be cast to object, which
defeats the purpose of strong typing.
Anonymous types can be initialized to include methods, but these might only be
of interest to linguists.
The single greatest value and the necessity of anonymous types is they support
creating single-use elements and composite types returned by LINQ queries
without the need for the programmer to fully define these types in static code.
That is, the designers can focus significantly on primary domain types, and the
programmers can still create single-use anonymous types ad hoc, letting the
compiler write the class definition. Finally, because anonymous types are
immutable—think no property setters—two separately defined anonymous types with
the same field values are considered equal.
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Book Excerpt: LINQ Unleashed for C#
Reproduced from the book
LINQ Unleashed for C#. Copyrightã 2008, Pearson Education, Inc., 800
East 96th Street, Indianapolis, IN 46240.
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Programming with Anonymous Types
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Databinding Anonymous Types
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Testing Anonymous Type Equality
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Using Anonymous Types with LINQ Queries
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Introducing Generic Anonymous Methods
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