add scala 2&3 tables arround code in num 7 (#2568)

Author: benluo

_overviews/scala3-book/taste-vars-data-types.md

@@ -9,10 +9,8 @@ next-page: taste-control-structures
 ---
 
 
-
 This section provides a look at Scala variables and data types.
 
-
 ## Two types of variables
 
 When you create a new variable in Scala, you declare whether the variable is immutable or mutable:
@@ -38,43 +36,64 @@ When you create a new variable in Scala, you declare whether the variable is imm
 
 These examples show how to create `val` and `var` variables:
 
+{% tabs var-express-1 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-1 %}
+
 ```scala
 // immutable
 val a = 0
 
 // mutable
 var b = 1
 ```
+{% endtab %}
+{% endtabs %}
 
 In an application, a `val` can’t be reassigned.
 You’ll cause a compiler error if you try to reassign one:
 
+{% tabs var-express-2 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-2 %}
+
 ```scala
 val msg = "Hello, world"
 msg = "Aloha"   // "reassignment to val" error; this won’t compile
 ```
+{% endtab %}
+{% endtabs %}
 
 Conversely, a `var` can be reassigned:
 
+{% tabs var-express-3 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-3 %}
+
 ```scala
 var msg = "Hello, world"
 msg = "Aloha"   // this compiles because a var can be reassigned
 ```
-
-
+{% endtab %}
+{% endtabs %}
 
 ## Declaring variable types
 
 When you create a variable you can explicitly declare its type, or let the compiler infer the type:
 
+{% tabs var-express-4 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-4 %}
+
 ```scala
 val x: Int = 1   // explicit
 val x = 1        // implicit; the compiler infers the type
 ```
+{% endtab %}
+{% endtabs %}
 
 The second form is known as _type inference_, and it’s a great way to help keep this type of code concise.
 The Scala compiler can usually infer the data type for you, as shown in the output of these REPL examples:
 
+{% tabs var-express-5 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-5 %}
+
 ```scala
 scala> val x = 1
 val x: Int = 1
@@ -85,19 +104,24 @@ val s: String = a string
 scala> val nums = List(1, 2, 3)
 val nums: List[Int] = List(1, 2, 3)
 ```
+{% endtab %}
+{% endtabs %}
 
 You can always explicitly declare a variable’s type if you prefer, but in simple assignments like these it isn’t necessary:
 
+{% tabs var-express-6 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-6 %}
+
 ```scala
 val x: Int = 1
 val s: String = "a string"
 val p: Person = Person("Richard")
 ```
+{% endtab %}
+{% endtabs %}
 
 Notice that with this approach, the code feels more verbose than necessary.
 
-
-
 {% comment %}
 TODO: Jonathan had an early comment on the text below: “While it might feel like this, I would be afraid that people automatically assume from this statement that everything is always boxed.” Suggestion on how to change this?
 {% endcomment %}
@@ -109,6 +133,9 @@ In Scala, everything is an object.
 
 These examples show how to declare variables of the numeric types:
 
+{% tabs var-express-7 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-7 %}
+
 ```scala
 val b: Byte = 1
 val i: Int = 1
@@ -117,38 +144,59 @@ val s: Short = 1
 val d: Double = 2.0
 val f: Float = 3.0
 ```
+{% endtab %}
+{% endtabs %}
 
 Because `Int` and `Double` are the default numeric types, you typically create them without explicitly declaring the data type:
 
+{% tabs var-express-8 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-8 %}
+
 ```scala
 val i = 123   // defaults to Int
 val j = 1.0   // defaults to Double
 ```
+{% endtab %}
+{% endtabs %}
 
 In your code you can also append the characters `L`, `D`, and `F` (and their lowercase equivalents) to numbers to specify that they are `Long`, `Double`, or `Float` values:
 
+{% tabs var-express-9 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-9 %}
+
 ```scala
 val x = 1_000L   // val x: Long = 1000
 val y = 2.2D     // val y: Double = 2.2
 val z = 3.3F     // val z: Float = 3.3
 ```
+{% endtab %}
+{% endtabs %}
 
 When you need really large numbers, use the `BigInt` and `BigDecimal` types:
 
+{% tabs var-express-10 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-10 %}
+
 ```scala
 var a = BigInt(1_234_567_890_987_654_321L)
 var b = BigDecimal(123_456.789)
 ```
+{% endtab %}
+{% endtabs %}
 
 Where `Double` and `Float` are approximate decimal numbers, `BigDecimal` is used for precise arithmetic.
 
 Scala also has `String` and `Char` data types:
 
+{% tabs var-express-11 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-11 %}
+
 ```scala
 val name = "Bill"   // String
 val c = 'a'         // Char
 ```
-
+{% endtab %}
+{% endtabs %}
 
 ### Strings
 
@@ -162,28 +210,43 @@ Scala strings are similar to Java strings, but they have two great additional fe
 String interpolation provides a very readable way to use variables inside strings.
 For instance, given these three variables:
 
+{% tabs var-express-12 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-12 %}
+
 ```scala
 val firstName = "John"
 val mi = 'C'
 val lastName = "Doe"
 ```
+{% endtab %}
+{% endtabs %}
 
 You can combine those variables in a string like this:
 
+{% tabs var-express-13 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-13 %}
+
 ```scala
 println(s"Name: $firstName $mi $lastName")   // "Name: John C Doe"
 ```
+{% endtab %}
+{% endtabs %}
 
 Just precede the string with the letter `s`, and then put a `$` symbol before your variable names inside the string.
 
 To embed arbitrary expressions inside a string, enclose them in curly braces:
 
+{% tabs var-express-14 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-14 %}
+
 ``` scala
 println(s"2 + 2 = ${2 + 2}")   // prints "2 + 2 = 4"
 
 val x = -1
 println(s"x.abs = ${x.abs}")   // prints "x.abs = 1"
 ```
+{% endtab %}
+{% endtabs %}
 
 The `s` that you place before the string is just one possible interpolator.
 If you use an `f` instead of an `s`, you can use `printf`-style formatting syntax in the string.
@@ -194,15 +257,17 @@ For instance, some database libraries define the very powerful `sql` interpolato
 
 Multiline strings are created by including the string inside three double-quotes:
 
+{% tabs var-express-15 class=tabs-scala-version %}
+{% tab 'Scala 2 and 3' for=var-express-15 %}
+
 ```scala
 val quote = """The essence of Scala:
                Fusion of functional and object-oriented
                programming in a typed setting."""
 ```
+{% endtab %}
+{% endtabs %}
 
 > For more details on string interpolators and multiline strings, see the [“First Look at Types” chapter][first-look].
 
-
-
-
 [first-look]: {% link _overviews/scala3-book/first-look-at-types.md %}