Throw new exception using object initializer

Question

Let's consider this code :

try
{
    return new ClassA.GetStuff();
}
catch (Exception e)
{
    throw new MyException
        ("message", e)
        {SomeMyExceptionProperty = "something"};
}

When throwing MyException, how the object initialization is done? Like this :

MyException myException = new MyException("message", e);
myException.SomeMyExceptionProperty = "something";
throw myException;

or like this (so the SomeMyExceptionProperty is not initialized) :

MyException myException = new MyException("message", e);
throw myException;
myException.SomeMyExceptionProperty = "something"; //unreachable code

I think that the first behavior is used, like for a return statement, but where is the official documentation about this?

Jon Skeet · Accepted Answer · 2016-02-22 10:34:48Z

7

As ever, the official documentation is the C# specification.

The important part is that this is just a throw statement. It has two parts (in this case):

The keyword throw
An expression which determines the exception to throw

In this case, the expression includes an object initializer. The whole expression is evaluated before anything is thrown.

From section 8.9.5 of the C# 5 spec:

A throw statement with an expression throws the value produced by evaluating the expression.

Evaluating the expression

new MyException
    ("message", e)
    {SomeMyExceptionProperty = "something"}

... includes assigning the value "something" to the SomeMyExceptionProperty.

answered Feb 22, 2016 at 10:34

Jon Skeet

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