C#•4y ago

Method works when dependent Method never called?

I am following a Pluralsight tutorial on ASP.NET Fundamentals and we've just created this hard-coded data repository to work from:

public class MockPieRepository : IPieRepository
{
    private readonly ICategoryRepository _categoryRepository = new MockCategoryRepository();

    public IEnumerable<Pie> AllPies =>
        new List<Pie>
        {
            new Pie {PieId = 1, etc},
            new Pie {PieId = 2, etc}
        };

   public IEnumerable<Pie> PiesOfTheWeek
    {
     get
        {
            return AllPies.Where(p => p.IsPieOfTheWeek);
        }
    }
}

public class MockPieRepository : IPieRepository
{
    private readonly ICategoryRepository _categoryRepository = new MockCategoryRepository();

    public IEnumerable<Pie> AllPies =>
        new List<Pie>
        {
            new Pie {PieId = 1, etc},
            new Pie {PieId = 2, etc}
        };

   public IEnumerable<Pie> PiesOfTheWeek
    {
     get
        {
            return AllPies.Where(p => p.IsPieOfTheWeek);
        }
    }
}

I understand what both of these methods do but I don't understand how the

PiesOfTheWeek

PiesOfTheWeek

method would currently work as the

AllPies

AllPies

has never been called and not called in any constructor? I would expect

PiesOfTheWeek

PiesOfTheWeek

to return Null when it tries it's Where statement.

Also, shouldn't

AllPies

AllPies

have

()

()

when it's used in

PiesOfTheWeek

PiesOfTheWeek

?

Thank you in advance!

DarylOP•9/10/22, 5:01 PM

...Thinking out loud here but is

AllPies

AllPies

actually just a property/field? I don't really understand the , in context I think it's a lambda expression but I've never found a description I understand...

DarylOP•9/10/22, 5:08 PM

I am being an idiot -

PiesOfTheWeek

PiesOfTheWeek

is a property. I see that now, still not quite sure about

AllPies

AllPies

and the though.

becquerel•9/10/22, 6:31 PM

AllPies is actually using alternate syntax for a normal method -- it's creating a new every time it's referenced, just like a method would do

becquerel•9/10/22, 6:31 PM

that's why you can call it whenever

becquerel•9/10/22, 6:31 PM

it's not stateful, it's a method returning a value

becquerel•9/10/22, 6:32 PM

incidentally, for the same reason you could rewrite PiesOfTheWeek like this:

becquerel•9/10/22, 6:32 PM

get

get

ers are really just methods, and properties are also really just methods, so they're interchangeable

DarylOP•9/10/22, 6:54 PM

Thank you! I didn't know a new would be created every time

AllPies

AllPies

is referenced. Is that unique to Dependancy Injection? I was under the impression in something like a Console App,

PiesOfTheWeek

PiesOfTheWeek

would error trying to return

becquerel•9/10/22, 6:55 PM

that's just a part of the C# language - you're not doing any dependency injection in that code snippet

DarylOP•9/10/22, 6:55 PM

AllPies

AllPies

is a method and it's being called everytime? But shouldn't it be when it's called?

becquerel•9/10/22, 6:56 PM

the

()

()

are not necessary when you use the syntax

becquerel•9/10/22, 6:56 PM

the idea is that, from outside the class, these things are indistinguishable from 'normal' properties

becquerel•9/10/22, 6:57 PM

which also don't have

()

()

DarylOP•9/10/22, 6:57 PM

Oh right ok. This counts as an Expression Lambda?

becquerel•9/10/22, 6:57 PM

the symbol is called a lambda, but this example isn't an expression tree

becquerel•9/10/22, 6:58 PM

(more technically, a lambda is only when you use the to create a new method on-the-fly, like you do in

but that distinction in not very meaningful)

DarylOP•9/10/22, 6:59 PM

Ok, so this Syntax doesn't count as a Lambda in anyway? I get myself really confused with the

becquerel•9/10/22, 6:59 PM

not technically. but most people would refer to it as such

becquerel•9/10/22, 7:00 PM

the => is confusing at first but makes sense eventually

becquerel•9/10/22, 7:00 PM

in , everything before => are parameters to the method, everything after is the actual method

DarylOP•9/10/22, 7:02 PM

Yeah I can see how it works in Linq queries and anonymous methods but this feels new

becquerel•9/10/22, 7:02 PM

yeah, it is

becquerel•9/10/22, 7:02 PM

it's a more recent addition to the language

becquerel•9/10/22, 7:03 PM

they co-opted the LINQ syntax because they don't like introducing new symbols

becquerel•9/10/22, 7:03 PM

under the hood they don't do the same thing

DarylOP•9/10/22, 7:04 PM

If I see it for a property - Is it only read only? Just looking at this:
https://stackoverflow.com/questions/40282424/what-does-operator-mean-in-a-property-in-c

And the example is:

Translates to this:

becquerel•9/10/22, 7:04 PM

correct

becquerel•9/10/22, 7:04 PM

those two are equivalent

becquerel•9/10/22, 7:05 PM

and because there's no

set

set

, it's read-only

DarylOP•9/10/22, 7:05 PM

But there's no way to do a and do a

set

set

right?

becquerel•9/10/22, 7:06 PM

well

becquerel•9/10/22, 7:06 PM

you can do this

DarylOP•9/10/22, 7:06 PM

Ugh

DarylOP•9/10/22, 7:06 PM

Now I'm lost again. Lol. Ok.

becquerel•9/10/22, 7:06 PM

it happens

becquerel•9/10/22, 7:07 PM

i'm happy to go into detail on any bits

DarylOP•9/10/22, 7:08 PM

I'm trying not to waste your time but at the same time I'm struggling.

My understanding up until that last code snippet is that is used for:

LINQ
Anonymous Functions which are only one line/don't really need to be named
And now, Read Only Properties which don't have a

But then you've thrown that last one in which has confused me a bit again

becquerel•9/10/22, 7:09 PM

just for reference, LINQ is anonymous functions

becquerel•9/10/22, 7:09 PM

that is, is using an anonymous function for Where()

DDaryl I'm trying not to waste your time but at the same time I'm struggling. My under...

becquerel•9/10/22, 7:10 PM

the last snippet i showed is the 'long-form' way of writing properties

becquerel•9/10/22, 7:10 PM

it was the first form added to the language

becquerel•9/10/22, 7:10 PM

=> is still the same concept of describing a function, though

becquerel•9/10/22, 7:11 PM

means 'run this function every time someone tries to set the value of this property'

becquerel•9/10/22, 7:11 PM

the keyword stands in for whatever they're trying to set it to

DarylOP•9/10/22, 7:13 PM

So why not

Syntax may be off, I'm still reasonably new to C# but basically just ?

becquerel•9/10/22, 7:13 PM

you can do exactly that too

becquerel•9/10/22, 7:13 PM

DarylOP•9/10/22, 7:13 PM

So what's the advantage of the