Expression.Convert Method

Definition

Namespace:

System.Linq.Expressions

Assembly:

System.Linq.Expressions.dll

Creates a UnaryExpression that represents a type conversion operation.

Overloads

Convert(Expression, Type)	Creates a UnaryExpression that represents a type conversion operation.
Convert(Expression, Type, MethodInfo)	Creates a UnaryExpression that represents a conversion operation for which the implementing method is specified.

Convert(Expression, Type)

Source:

UnaryExpression.cs

Creates a UnaryExpression that represents a type conversion operation.

public:
 static System::Linq::Expressions::UnaryExpression ^ Convert(System::Linq::Expressions::Expression ^ expression, Type ^ type);

public static System.Linq.Expressions.UnaryExpression Convert (System.Linq.Expressions.Expression expression, Type type);

static member Convert : System.Linq.Expressions.Expression * Type -> System.Linq.Expressions.UnaryExpression

Public Shared Function Convert (expression As Expression, type As Type) As UnaryExpression

Parameters

expression

Expression

An Expression to set the Operand property equal to.

type

Type

A Type to set the Type property equal to.

Returns

UnaryExpression

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

Exceptions

ArgumentNullException

expression or type is null.

InvalidOperationException

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

Examples

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

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

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

// Print out the expression.
Console.WriteLine(convertExpr.ToString());

// The following statement first creates an expression tree,
// then compiles it, and then executes it.
Console.WriteLine(Expression.Lambda<Func<Int16>>(convertExpr).Compile()());

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

' Add the following directive to your file:
' Imports System.Linq.Expressions 

' This expression represents a type conversion operation.        
Dim convertExpr As Expression = Expression.Convert(
                            Expression.Constant(5.5),
                            GetType(Int16)
                        )

' Print the expression.
Console.WriteLine(convertExpr.ToString())

' The following statement first creates an expression tree,
' then compiles it, and then executes it.
Console.WriteLine(Expression.Lambda(Of Func(Of Int16))(convertExpr).Compile()())

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

Remarks

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.

Convert(Expression, Type, MethodInfo)

Source:

UnaryExpression.cs

Creates a UnaryExpression that represents a conversion operation for which the implementing method is specified.

public:
 static System::Linq::Expressions::UnaryExpression ^ Convert(System::Linq::Expressions::Expression ^ expression, Type ^ type, System::Reflection::MethodInfo ^ method);

public static System.Linq.Expressions.UnaryExpression Convert (System.Linq.Expressions.Expression expression, Type type, System.Reflection.MethodInfo? method);

static member Convert : System.Linq.Expressions.Expression * Type * System.Reflection.MethodInfo -> System.Linq.Expressions.UnaryExpression

Public Shared Function Convert (expression As Expression, type As Type, method As MethodInfo) As UnaryExpression

Parameters

expression

Expression

An Expression to set the Operand property equal to.

type

Type

A Type to set the Type property equal to.

method

MethodInfo

A MethodInfo to set the Method property equal to.

Returns

UnaryExpression

A UnaryExpression that has the NodeType property equal to Convert and the Operand, Type, and Method properties set to the specified values.

Exceptions

ArgumentNullException

expression or type is null.

ArgumentException

method is not null and the method it represents returns void, is not static (Shared in Visual Basic), or does not take exactly one argument.

InvalidOperationException

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

-or-

expression.Type is not assignable to the argument type of the method represented by method.

-or-

The return type of the method represented by method is not assignable to type.

-or-

expression.Type or type is a nullable value type and the corresponding non-nullable value type does not equal the argument type or the return type, respectively, of the method represented by method.

AmbiguousMatchException

More than one method that matches the method description was found.

Remarks

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 method is not null, it is the implementing method. It must represent a non-void, static (Shared in Visual Basic) method that takes one argument.

• Otherwise, 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 either or both of expression.Type or type are 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.