.Net lambda expression— where did this parameter come from?

Question

I\'m a lambda newbie, so if I\'m missing vital information in my description please tell me. I\'ll keep the example as simple as possible.

I\'m going over someone

Answer 1

p is just a dummy name, it's the name of the parameter like in any method. You could name it x or Fred, if you like.

Remember, lambda expressions are just very, very special anonymous methods.

In regular methods you have parameters, and they have names:

public double GetQuantitysaved(ViewModelBase p) {
    return QuantitySaved;
}

In anonymous methods you have parameters, and they have names:

delegate(ViewModelBase p) { return QuantitySaved; }

In lambda expressions you have parameters, and they have names:

p => QuantitySaved

The p here plays the same role in all three versions. You can name it whatever you want. It's just the name of a parameter to the method.

In the last case, the compiler does a lot of work to figure out that p represents a parameter of type ViewModelBase so that p => QuantitySaved can play the role of

Expression> property

For fun I changed the code from p to this, since SampleViewModel inherits from ViewModelBase, but I was met with a series of compiler errors, the first one of which stated Invalid expression term '=>' This confused me a bit since I thought that would work.

Well, this is not a valid parameter name because it's a reserved keyword. It's best to think of p => QuantitySaved as

delegate(ViewModelBase p) { return QuantitySaved; }

until you get comfortable with the idea. In this case, this could never be substituted in for p as it is not a valid parameter name.