object constructor - shorthand property syntax

Question

A few months ago i read about a technique so that if there paramaters you passed in matched the local variables then you could use some short hand syntax to set them. To avoid this:

public string Method(p1, p2, p3)
{
    this.p1 = p1;
    this.p2 = p2;
    this.p3 = p3;
}

Any ideas?

Answer 1

You might be thinking of the "object initializer" in C#, where you can construct an object by setting the properties of the class, rather than using a parameterized constructor.

I'm not sure it can be used in the example you have since your "this" has already been constructed.

Answer 2

You may be thinking about the new object initializer syntax in C# 3.0. It looks like this:

var foo = new Foo { Bar = 1, Fizz = "hello" };

So that's giving us a new instance of Foo, with the "Bar" property initialized to 1 and the "Fizz" property to "hello".

The trick with this syntax is that if you leave out the "=" and supply an identifier, it will assume that you're assigning to a property of the same name. So, for example, if I already had a Foo instance, I could do this:

var foo2 = new Foo { foo1.Bar, foo1.Fizz };

This, then, is getting pretty close to your example. If your class has p1, p2 and p3 properties, and you have variables with the same name, you could write:

var foo = new Foo { p1, p2, p3 };

Note that this is for constructing instances only - not for passing parameters into methods as your example shows - so it may not be what you're thinking of.