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C#•2y 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 method would currently work as the AllPies has never been called and not called in any constructor? I would expect PiesOfTheWeek to return Null when it tries it's Where statement. Also, shouldn't AllPies have () when it's used in PiesOfTheWeek? Thank you in advance!

60 Replies

Daryl•2y ago

...Thinking out loud here but is 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... I am being an idiot - PiesOfTheWeek is a property. I see that now, still not quite sure about AllPies and the => though. 🙂

Becquerel•2y ago

AllPies is actually using alternate syntax for a normal method -- it's creating a new IEnumerable<Pie> every time it's referenced, just like a method GetAllPies() would do that's why you can call it whenever it's not stateful, it's a method returning a value incidentally, for the same reason you could rewrite PiesOfTheWeek like this: public IEnumerable<Pie> PiesOfTheWeek => AllPies.Where(p => p.IsPieOfTheWeek); geters are really just methods, and => properties are also really just methods, so they're interchangeable 🙂

Daryl•2y ago

Thank you! I didn't know a new IEnumerable<Pie> would be created every time AllPies is referenced. Is that unique to Dependancy Injection? I was under the impression in something like a Console App, PiesOfTheWeek would error trying to return AllPies.Where(...)

Becquerel•2y ago

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

Daryl•2y ago

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

Becquerel•2y ago

the () are not necessary when you use the => syntax the idea is that, from outside the class, these things are indistinguishable from 'normal' properties which also don't have ()

Daryl•2y ago

Oh right ok. This counts as an Expression Lambda?

Becquerel•2y ago

the => symbol is called a lambda, but this example isn't an expression tree (more technically, a lambda is only when you use the => to create a new method on-the-fly, like you do in .Where() - but that distinction in not very meaningful)

Daryl•2y ago

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

Becquerel•2y ago

not technically. but most people would refer to it as such the => is confusing at first but makes sense eventually in Where(p => p.IsPieOfTheWeek);, everything before => are parameters to the method, everything after is the actual method

Daryl•2y ago

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

Becquerel•2y ago

yeah, it is it's a more recent addition to the language they co-opted the LINQ syntax because they don't like introducing new symbols under the hood they don't do the same thing

Daryl•2y ago

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:

public bool property => method():

public bool property => method():

Translates to this:

public bool property {
    get {
        return method();
    }
}

public bool property {
    get {
        return method();
    }
}

Becquerel•2y ago

correct those two are equivalent and because there's no set, it's read-only

Daryl•2y ago

But there's no way to do a => and do a set right?

Becquerel•2y ago

well

    private string _myString;

    public string MyString
    {
        get => _myString;
        set => _myString = value;
    }

    private string _myString;

    public string MyString
    {
        get => _myString;
        set => _myString = value;
    }

you can do this

Daryl•2y ago

Ugh Now I'm lost again. Lol. Ok.

Becquerel•2y ago

😄 it happens i'm happy to go into detail on any bits

Daryl•2y ago

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

Becquerel•2y ago

just for reference, LINQ is anonymous functions that is, .Where(x => x.IsSomething) is using an anonymous function for Where() the last snippet i showed is the 'long-form' way of writing properties it was the first form added to the language => is still the same concept of describing a function, though set => _myString = value; means 'run this function every time someone tries to set the value of this property' the value keyword stands in for whatever they're trying to set it to

Daryl•2y ago

So why not

private string _myString;

public string MyString
{
  get { _myString };
  set { _myString = Value};
}

private string _myString;

public string MyString
{
  get { _myString };
  set { _myString = Value};
}

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

Becquerel•2y ago

you can do exactly that too 🙂

Daryl•2y ago

So what's the advantage of the =>

Becquerel•2y ago

more concise for the get you have to write return as well

    private string _myString;

    public string MyString
    {
        get { return _myString; }
        set { _myString = value; }
    }

    private string _myString;

    public string MyString
    {
        get { return _myString; }
        set { _myString = value; }
    }

c# has a lot of syntax sugar like this -- functionally identical, but just a little tidier or fewer keystrokes

Daryl•2y ago

So basically => translates to what is on the right of me is a codeblock but it's only one line ?

Becquerel•2y ago

mhm... not necessarily!

Daryl•2y ago

😢

Becquerel•2y ago

    public void DoSomething()
    {
        Action blah = () =>
        {
            Console.WriteLine("Hello from a multi-line lambda");
        };

        blah.Invoke();
    }

    public void DoSomething()
    {
        Action blah = () =>
        {
            Console.WriteLine("Hello from a multi-line lambda");
        };

        blah.Invoke();
    }

normally, yes, lambdas are one line but they can also point at { } blocks which can contain whatever you like this is because the { } block is treated as one statement

Daryl•2y ago

I haven't seen Action or Invoke yet. 😅

Becquerel•2y ago

heh sorry

Daryl•2y ago

No problem, I appreciate your help!

Becquerel•2y ago

that's basically how you assign a lambda to a variable which lets you pass them around like anything else

Func<int, bool> isEven = x => x % 2 == 0;
var myList = new List<int>() { 3, 5, 2, 10 } ;
var evens = myList.Where(isEven);

Func<int, bool> isEven = x => x % 2 == 0;
var myList = new List<int>() { 3, 5, 2, 10 } ;
var evens = myList.Where(isEven);

a similar concept

Daryl•2y ago

So I can do this:

public int timesBytwo() x => x * 2;
// timesByTwo(4) = 8
public int number => 4;
// number is now 8 but this is a read-only field, not a variable?
public int crazyMaths() x => {
  x += 2;
  x -= 1;
  x;
}
// crazyMaths(1) would return 2?

public int timesBytwo() x => x * 2;
// timesByTwo(4) = 8
public int number => 4;
// number is now 8 but this is a read-only field, not a variable?
public int crazyMaths() x => {
  x += 2;
  x -= 1;
  x;
}
// crazyMaths(1) would return 2?

Becquerel•2y ago

ah, not quite public int timesBytwo() x => x * 2; this would complain because it wouldn't know what 'x' is

Daryl•2y ago

Yeah I was just thinking how come you don't have to say what the data type is 😕

Becquerel•2y ago

the correct form would be public int timesBytwo(int x) => x * 2;

Daryl•2y ago

Ok, that makes sense

Becquerel•2y ago

technically, you always have to say the data type. it's just that sometimes it can infer what you mean and let you skip it the proper form of Where, for instance, is myListOfInts.Where<int>(x => ...); but because the compiler already knows your list is a List<int> (or whatever), it lets you skip it on the Where it doesn't have that information in timesByTwo for your crazyMaths method... if you use a { } block, you have to go back to using the return statement unfortunately rust lets you omit it, but not c# yet 😄

Daryl•2y ago

Ok so I'm almost there... But what's the point in using => if you're going to do a multi-line.. Thing?

Becquerel•2y ago

sometimes you need to use a => but want to do something on multiple lines, basically it's not a common thing but you can do it if you have a really complex thing you want to check in a Where, for instance, you can do it there so you don't have a line stretching out super-long

Daryl•2y ago

So in the above examples they should be this?

public int timesBytwo(int x) => x * 2;
// timesByTwo(4) = 8
public int number => 4;
// number is now 8 but this is a read-only field, not a variable?
public int crazyMaths(int x) => {
  x += 2;
  x -= 1;
  return x;
}
// crazyMaths(1) would return 2?

public int timesBytwo(int x) => x * 2;
// timesByTwo(4) = 8
public int number => 4;
// number is now 8 but this is a read-only field, not a variable?
public int crazyMaths(int x) => {
  x += 2;
  x -= 1;
  return x;
}
// crazyMaths(1) would return 2?

Becquerel•2y ago

oh, this is my bad for not catching it but you aren't allowed the => { } syntax for methods so instead it'd just be

public int crazyMaths(int x)
{
  x += 2;
  x -= 1;
  return x;
}

public int crazyMaths(int x)
{
  x += 2;
  x -= 1;
  return x;
}

as normal also

public int number => 4;
// number is now 8 but this is a read-only field, not a variable?

public int number => 4;
// number is now 8 but this is a read-only field, not a variable?

i'm not sure why you say number is now 8 here

Daryl•2y ago

LOL because I'm an idiot. My bad Meant to say 4

Becquerel•2y ago

it's not correct to say this is a read-only field -- it's a method that returns the new value of 4 every time. nothing is ever 'stored' lol easily done

Daryl•2y ago

Ok so whilst it makes sense, that confuses me with that stackoverflow link I sent earlier:

public bool property => method();
// Is the same as....
public bool property {
    get {
        return method();
    }
}

public bool property => method();
// Is the same as....
public bool property {
    get {
        return method();
    }
}

Isn't property technically a method then?

Becquerel•2y ago

yes. all properties are methods every property is literally just syntax sugar for methods if you go and look at java code, they don't have this syntax sugar so they literally have to write out get_myField() for everything it's a streamlining of that

Daryl•2y ago

Oh! Mindblown.

Becquerel•2y ago

yep! 😄 when you compile your code, it also literally turns properties back into those methods

Daryl•2y ago

That little nugget of info has made everything slot into place now I think I get it! Although two questions

public bool property => method()

public bool property => method()

Will still show up in Intellisense/Autocomplete as a Property? Not a method right? If you're not sure no worries I just didn't want to make a whole new project to check. Why don't you need () for the methods when you use => E.g

public bool myMethod => return true;
// I thought it should be:
public bool myMethod() => return true;

public bool myMethod => return true;
// I thought it should be:
public bool myMethod() => return true;

Becquerel•2y ago

1. yes, it'll show up as a property. that's what missing out the () does, if it had them it'd be parsed as a method with zero arguments 2. because the () is for listing the parameters to the anonymous method, and in those examples, there are either no parameters or they'd go in the () before the => to show what i mean...

Action<string, bool> blah = (s, b) => // do something with the string and bool...;
blah.Invoke("hello", true);

Action<string, bool> blah = (s, b) => // do something with the string and bool...;
blah.Invoke("hello", true);

in this example the anonymous method takes two arguments and so they're listed in the ()

Daryl•2y ago

So really if I'm doing a property I should exclude the () and if I'm doing a method I should include it, even if I'm not passing through any arguments, just so intellisense picks it up?

Becquerel•2y ago

yeah this is where it goes into matters of style a bit - when should something be a property, when should it be a method? i can explain my feelings on that but it's subjective also, just noticed public bool myMethod() => return true; remember that in this circumstance, you don't need return

Daryl•2y ago

Ah, only need return when it's multi-line Ok Thank you I think this all makes alot more sense And that explains why in the code I was copying from PluralSight, it wasn't returning a null because it's technically just a method ...Even though the method doesn't have () when it's called either - Because it's actually a property which behind the scenes, is a method. 😅

Becquerel•2y ago

agooglethumbsup

really only has three fundamentals variables, methods and classes

Daryl•2y ago

Ahh ok, yeah I find it interesting that I can write code and it works but there's still so many things I don't really know about. It doesn't help when they add loads of new things in each new version - Now you don't even have to use using statements?!

Becquerel•2y ago

oh totally it's easier to keep up when you're good with the language, but yeah if it helps, also, there's never any breaking changes the new stuff is always just syntax sugars and such

Daryl•2y ago

I think that's what I'm trying to say. It's great when you're good with the language and they're introducing things in dribs and drabs but when you're trying to get into the language and everything keeps changing it's really damn hard to keep up with. So many tutorials are out of date so you can easily end up learning the older ways of doing things. Thank you for all your help, I really appreciate it. Learned a LOT! Thanks

Becquerel•2y ago

yeah... it is hard. but when you have a 20-year-old language it's a difficult problem to avoid and no problem! feel free to DM me if you have any more questions

Daryl•2y ago

Thank you, I appreciate it 🙂 Tomorrow I'll continue with ASP.Net, what a minefield that is

Becquerel•2y ago

oh god, it is

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