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Expression.Convert Method (Expression, Type)

Creates a UnaryExpression that represents a type conversion operation.

Namespace:  System.Linq.Expressions
Assembly:  System.Core (in System.Core.dll)

public static UnaryExpression Convert(
	Expression expression,
	Type type
)

Parameters

expression
Type: System.Linq.Expressions.Expression
An Expression to set the Operand property equal to.
type
Type: System.Type
A Type to set the Type property equal to.

Return Value

Type: System.Linq.Expressions.UnaryExpression
A UnaryExpression that has the NodeType property equal to Convert and the Operand and Type properties set to the specified values.

ExceptionCondition
ArgumentNullException

expression or type is null.

InvalidOperationException

No conversion operator is defined between expression.Type and type.

The Method property of the resulting UnaryExpression is set to the implementing method. The IsLiftedToNull property is false. If the node is lifted, IsLifted is true. Otherwise, it is false.

Implementing Method

The following rules determine the implementing method for the operation:

  • If either expression.Type or type is a user-defined type that defines an implicit or explicit conversion operator, the MethodInfo that represents that operator is the implementing method.

  • Otherwise:

    • If both expression.Type and type represent numeric or Boolean types, or nullable or non-nullable enumeration types, the implementing method is null.

    • If either expression.Type or type is a reference type and an explicit boxing, unboxing, or reference conversion exists from expression.Type to type, the implementing method is null.

Lifted versus Non-Lifted

If the implementing method is not null:

  • If expression.Type is assignable to the argument type of the implementing method and the return type of the implementing method is assignable to type, the node is not lifted.

  • If one or both of expression.Type or type is a nullable value type and the corresponding non-nullable value types are equal to the argument type and the return type of the implementing method respectively, the node is lifted.

If the implementing method is null:

  • If both expression.Type and type are non-nullable, the node is not lifted.

  • Otherwise the node is lifted.

The following code example shows how to create an expression that represents a type convertion operation.


       // Add the following directive to your file:
       // using System.Linq.Expressions;  

       // This expression represents a type convertion operation. 
       Expression convertExpr = Expression.Convert(
                                   Expression.Constant(5.5),
                                   typeof(Int16)
                               );

       // Print out the expression.
       outputBlock.Text += convertExpr.ToString() + "\n";

       // The following statement first creates an expression tree,
       // then compiles it, and then executes it.
       outputBlock.Text += Expression.Lambda<Func<Int16>>(convertExpr).Compile()() + "\n";

       // This code example produces the following output:
       //
       // Convert(5.5)
       // 5



Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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