Expression Tree Tutorial IfThenElse

The Expression.IfThenElse method creates a ConditionalExpression that represents a conditional block with if and else statements. For example, you have the following code.

int num = 60;

if(num > 10)
{
    Console.WriteLine("num is greater than 10");
}
else
{
    Console.WriteLine("num is less than or equan to 10");
}

Here is the code that is required to build the same functionality using expression tree.

int num = 60;

var testCondition = Expression.Constant(num > 10);
var ifTrueBlock = WriteLineExpression("num is greater than 10");
var ifFalseBlock = WriteLineExpression("num is less than or equal to 10");

var ifThenElseExpr = Expression.IfThenElse(
    testCondition,
    ifTrueBlock,
    ifFalseBlock);

Expression.Lambda<Action>(ifThenElseExpr).Compile()();

This example shows how to create an expression that represents an if-else block. Here is the code for WriteLineExpression method

public static Expression WriteLineExpression(string s)
{
    return Expression.Call(null,
       typeof(Console).GetMethod("WriteLine", new Type[] { typeof(String) }),
       Expression.Constant(s));
}

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