ParameterExpression Class

Definition

Namespace:

System.Linq.Expressions

Assembly:

System.Linq.Expressions.dll

Source:

ParameterExpression.cs

Represents a named parameter expression.

public ref class ParameterExpression : System::Linq::Expressions::Expression

public class ParameterExpression : System.Linq.Expressions.Expression

type ParameterExpression = class
    inherit Expression

Public Class ParameterExpression
Inherits Expression

Inheritance

Object

Expression

ParameterExpression

Examples

The following example demonstrates how to create a MethodCallExpression object that prints the value of a ParameterExpression object by using the Parameter method.

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

// Creating a parameter for the expression tree.
ParameterExpression param = Expression.Parameter(typeof(int));

// Creating an expression for the method call and specifying its parameter.
MethodCallExpression methodCall = Expression.Call(
    typeof(Console).GetMethod("WriteLine", new Type[] { typeof(int) }),
    param
);

// The following statement first creates an expression tree,
// then compiles it, and then runs it.
Expression.Lambda<Action<int>>(
    methodCall,
    new ParameterExpression[] { param }
).Compile()(10);

// This code example produces the following output:
//
// 10

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

' Creating a parameter for the expression tree.
Dim param As ParameterExpression = Expression.Parameter(GetType(Integer))

' Creating an expression for the method call and specifying its parameter.
Dim methodCall As MethodCallExpression = Expression.Call(
        GetType(Console).GetMethod("WriteLine", New Type() {GetType(Integer)}),
        param
    )

' Compiling and invoking the methodCall expression.
Expression.Lambda(Of Action(Of Integer))(
    methodCall,
    New ParameterExpression() {param}
).Compile()(10)
' This code example produces the following output:
'
' 10

Remarks

Use the Parameter factory method to create a ParameterExpression.

The value of the NodeType property of a ParameterExpression object is Parameter.

Properties

CanReduce	Indicates that the node can be reduced to a simpler node. If this returns true, Reduce() can be called to produce the reduced form. (Inherited from Expression)
IsByRef	Indicates that this ParameterExpression is to be treated as a ByRef parameter.
Name	Gets the name of the parameter or variable.
NodeType	Returns the node type of this Expression.
Type	Gets the static type of the expression that this Expression represents.

Methods

Accept(ExpressionVisitor)	Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall(MethodCallExpression).
Equals(Object)	Determines whether the specified object is equal to the current object. (Inherited from Object)
GetHashCode()	Serves as the default hash function. (Inherited from Object)
GetType()	Gets the Type of the current instance. (Inherited from Object)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
Reduce()	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression)
ReduceAndCheck()	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression)
ReduceExtensions()	Reduces the expression to a known node type (that is not an Extension node) or just returns the expression if it is already a known type. (Inherited from Expression)
ToString()	Returns a textual representation of the Expression. (Inherited from Expression)
VisitChildren(ExpressionVisitor)	Reduces the node and then calls the visitor delegate on the reduced expression. The method throws an exception if the node is not reducible. (Inherited from Expression)