Expression Tree Tutorial Throw

You can build an expression tree which is throwing an exception by using Expression.Throw method. For example, you have the following code.

try
{
    Console.WriteLine("Before throwing exception");
    throw new DivideByZeroException();
    Console.WriteLine("After throwing exception");
}
catch (DivideByZeroException)
{
    Console.WriteLine("Catch block");
}

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

var tryBlock = Expression.Block(
    WriteLineExpression("Before throwing exception"),
    Expression.Throw(Expression.Constant(new DivideByZeroException())),
    WriteLineExpression("After throwing exception")
);

var catchBlock = Expression.Catch(
    typeof(DivideByZeroException),
    WriteLineExpression("Catch block")
);

TryExpression tryCatchExpr = Expression.TryCatch(tryBlock, catchBlock);

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

This example shows how to create an expression that contains a goto statement. 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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Expression Tree Tutorial Throw

Performance

Expression Evaluator