new classes tour #698

travissarles · 2017-02-15T14:45:32Z

No description provided.

julienrf · 2017-02-16T10:08:06Z

tutorials/tour/_posts/2017-02-13-classes.md

-Classes in Scala are parameterized with constructor arguments. The code above defines two constructor arguments, `x` and `y`; they are both visible in the whole body of the class.
+This `Point` class has four members: the variables `x` and `y` and the methods `move` and
+`toString`. Unlike many other languages, the primary constructor is in the class signature `(var x: Int, var y: Int)`. The `move` method takes two integer arguments but does not return a value (the return type `Unit` corresponds to `void` in Java-like languages). `toString`, on the other hand, does not take any parameters but returns a `String` value. Since `toString` overrides the inherited `toString` method, it is tagged with the `override` keyword.
+


Before jumping to secondary constructors I would put an example of instantiation and member calls.

julienrf · 2017-02-16T10:09:07Z

tutorials/tour/_posts/2017-02-13-classes.md

+class Point {
+  def this(x: Int, y: Int) {
+    this()
+    if (x > 100 || y > 100) println("Warning: Out of bounds")


This example is confusing since the x and y parameters are eventually discarded.

julienrf · 2017-02-16T10:09:32Z

tutorials/tour/_posts/2017-02-13-classes.md

  }
 }
 ```
+There are few requirements for auxiliary constructors:
+* They must start with `def this`
+* The parameters must _not_ be declared `val` or `var`


I would say “can not”

julienrf · 2017-02-16T10:11:00Z

tutorials/tour/_posts/2017-02-13-classes.md

+  override def toString: String =
+    s"Point: ($x, $y), Distance from origin: $distanceFromOrigin"
+  }
+```


Minor remark: usually private members are used to hide state from the outside. In your example that’s the opposite situation: private members are pure, while public members x and y are vars.

julienrf · 2017-02-16T10:11:50Z

tutorials/tour/_posts/2017-02-13-classes.md

+```
+
+You can also simply nest private methods inside of the public ones
+that use them:


I think this is a general point related to scopes more than classes. I’m not sure it’s best place is in this page.

julienrf · 2017-02-16T10:22:01Z

tutorials/tour/_posts/2017-02-13-classes.md


+Parameters without `val` or `var` are private values, visible only within the class and its subclasses.


Actually they are not visible from subclasses.

tpolecat · 2017-02-22T20:36:40Z

tutorials/tour/_posts/2017-02-13-classes.md

-Classes in Scala are static templates that can be instantiated into many objects at runtime.
-Here is a class definition which defines a class `Point`:
+Classes in Scala are blueprints for creating objects. They can contain methods,
+values, and variables, which are collectively called _members_.


They can also contain types, objects, traits, and classes which are also members.

I was going to add this later in a "nesting" tutorial but to be accurate, we need to mention it now and say "more on that later".

tpolecat · 2017-02-22T20:40:20Z

tutorials/tour/_posts/2017-02-13-classes.md

+
+## Defining a class
+A minimal class definition is simply the keyword `class` and
+an identifier:


It's important to note that class names should be capitalized because it's a universal convention and it has a downstream effect on pattern-matching.

A minimal class definition is simply the keyword class and an identifier. Class names should be capitalized.

Perhaps we should sprinkle naming conventions throughout the tour. It's easier than looking at a big naming-convention document, though both are important.

tpolecat · 2017-02-22T20:41:53Z

tutorials/tour/_posts/2017-02-13-classes.md

+
+val user1 = new User
+```
+The keyword `new` is used to create an instance of the class. `User` has an implicit constructor which takes no arguments because no constructor was defined. However, you'll often want a constructor and class body. Here is an example class definition for a point:


I would say "default" rather than "implicit" here to avoid confusion with implicit which is an unrelated concept.

tpolecat · 2017-02-22T20:46:16Z

tutorials/tour/_posts/2017-02-13-classes.md

 ```

-Classes in Scala are parameterized with constructor arguments. The code above defines two constructor arguments, `x` and `y`; they are both visible in the whole body of the class.
+This `Point` class has four members: the variables `x` and `y` and the methods `move` and
+`toString`. Unlike many other languages, the primary constructor is in the class signature `(var x: Int, var y: Int)`. The `move` method takes two integer arguments but does not return a value (the return type `Unit` corresponds to `void` in Java-like languages). `toString`, on the other hand, does not take any parameters but returns a `String` value. Since `toString` overrides the inherited `toString` method, it is tagged with the `override` keyword.


For "but does not return a value (the return type Unit corresponds to void in Java-like languages)" I suggest

and returns the Unit value (), which carries no information. This corresponds roughly with void in Java-like languages.

tpolecat · 2017-02-22T20:47:32Z

tutorials/tour/_posts/2017-02-13-classes.md

 ```

-Classes in Scala are parameterized with constructor arguments. The code above defines two constructor arguments, `x` and `y`; they are both visible in the whole body of the class.
+This `Point` class has four members: the variables `x` and `y` and the methods `move` and
+`toString`. Unlike many other languages, the primary constructor is in the class signature `(var x: Int, var y: Int)`. The `move` method takes two integer arguments but does not return a value (the return type `Unit` corresponds to `void` in Java-like languages). `toString`, on the other hand, does not take any parameters but returns a `String` value. Since `toString` overrides the inherited `toString` method, it is tagged with the `override` keyword.


toString overrides the inherited toString method

Inherited from what? We haven't talked about subclassing. Do we need to do this here?

I can maybe just add a link to the “unified types” page.

tpolecat · 2017-02-22T20:50:05Z

tutorials/tour/_posts/2017-02-13-classes.md

+
+This is also a good practice to enhance clarity.
+
+## Member scope


I suggest renaming this section something like Private Members and Getter/Setter Syntax.

SethTisue · 2017-02-28T03:33:41Z

tutorials/tour/_posts/2017-02-13-classes.md

+```
+class Point(val x: Int, val y: Int)
+val point = new Point(1, 2)
+val.x = 3  // <-- does not compile


I think you mean point.x, not val.x.

If it's not appropriate to introduce copy here, maybe at least add a note that links forward to where copy will be introduced?

added procedures as prereq

travissarles · 2017-03-14T15:04:52Z

@heathermiller ready to merge

SethTisue

I'm not very comfortable with having var so front-and-center here... but, this is certainly a huge improvement overall regardless, so I would say let's merge it, and perhaps come back and handle var differently in a future revision.

travissarles force-pushed the classes branch from 6333271 to 78db2e8 Compare February 15, 2017 19:14

julienrf reviewed Feb 16, 2017

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travissarles force-pushed the classes branch from 78db2e8 to 79fbccd Compare February 18, 2017 22:13

tpolecat reviewed Feb 22, 2017

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travissarles force-pushed the classes branch from 79fbccd to 082bc52 Compare February 24, 2017 16:19

SethTisue reviewed Feb 28, 2017

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Rewrote classes tour

3df470b

added procedures as prereq

travissarles force-pushed the classes branch from 082bc52 to 3df470b Compare February 28, 2017 13:32

SethTisue approved these changes Mar 14, 2017

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travissarles mentioned this pull request Mar 17, 2017

Rewrite tour of Scala #733

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SethTisue merged commit 978920c into scala:master Apr 4, 2017

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new classes tour #698

new classes tour #698

travissarles commented Feb 15, 2017

julienrf Feb 16, 2017

julienrf Feb 16, 2017

julienrf Feb 16, 2017

julienrf Feb 16, 2017

julienrf Feb 16, 2017

julienrf Feb 16, 2017

tpolecat Feb 22, 2017

travissarles Feb 23, 2017

tpolecat Feb 22, 2017

travissarles Feb 23, 2017

tpolecat Feb 22, 2017

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tpolecat Feb 22, 2017

julienrf Feb 23, 2017

tpolecat Feb 22, 2017

SethTisue Feb 28, 2017

travissarles commented Mar 14, 2017

SethTisue left a comment


		Parameters without `val` or `var` are private values, visible only within the class and its subclasses.


		This is also a good practice to enhance clarity.

		## Member scope

new classes tour #698

new classes tour #698

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travissarles commented Feb 15, 2017

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travissarles commented Mar 14, 2017

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