![\"Scala](\"https://docs.scala-lang.org/resources/images/tour/unified-types-diagram.svg\")
Tour of Scala
\n", "\n", "\n", "# Unified Types\n", "\n", "In Scala, all values have a type, including numerical values and functions. The diagram below illustrates a subset of the type hierarchy.\n", "\n", "\n",
"\n",
"## Scala Type Hierarchy ##\n",
"\n",
"[`Any`](http://www.scala-lang.org/api/2.12.1/scala/Any.ipynb) is the supertype of all types, also called the top type. It defines certain universal methods such as `equals`, `hashCode`, and `toString`. `Any` has two direct subclasses: `AnyVal` and `AnyRef`.\n",
"\n",
"`AnyVal` represents value types. There are nine predefined value types and they are non-nullable: `Double`, `Float`, `Long`, `Int`, `Short`, `Byte`, `Char`, `Unit`, and `Boolean`. `Unit` is a value type which carries no meaningful information. There is exactly one instance of `Unit` which can be declared literally like so: `()`. All functions must return something so sometimes `Unit` is a useful return type.\n",
"\n",
"`AnyRef` represents reference types. All non-value types are defined as reference types. Every user-defined type in Scala is a subtype of `AnyRef`. If Scala is used in the context of a Java runtime environment, `AnyRef` corresponds to `java.lang.Object`.\n",
"\n",
"Here is an example that demonstrates that strings, integers, characters, boolean values, and functions are all objects just like every other object:"
]
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"a string\n",
"732\n",
"c\n",
"true\n",
"ammonite.$sess.cmd0$Helper$$Lambda$2352/2102673157@2859fdff\n"
]
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"text/plain": [
"\u001b[36mlist\u001b[39m: \u001b[32mList\u001b[39m[\u001b[32mAny\u001b[39m] = \u001b[33mList\u001b[39m(\n",
" \u001b[32m\"a string\"\u001b[39m,\n",
" \u001b[32m732\u001b[39m,\n",
" \u001b[32m'c'\u001b[39m,\n",
" true,\n",
" ammonite.$sess.cmd0$Helper$$Lambda$2352/2102673157@2859fdff\n",
")"
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"source": [
"val list: List[Any] = List(\n",
" \"a string\",\n",
" 732, // an integer\n",
" 'c', // a character\n",
" true, // a boolean value\n",
" () => \"an anonymous function returning a string\"\n",
")\n",
"\n",
"list.foreach(element => println(element))"
]
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"It defines a variable `list` of type `List[Any]`. The list is initialized with elements of various types, but they all are instance of `scala.Any`, so you can add them to the list.\n",
"\n",
"Here is the output of the program:"
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"```\n",
"a string\n",
"732\n",
"c\n",
"true\n",
"![\"Scala](\"https://docs.scala-lang.org/resources/images/tour/type-casting-diagram.svg\")
\n",
"\n",
"For example:"
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"\u001b[36mx\u001b[39m: \u001b[32mLong\u001b[39m = \u001b[32m987654321L\u001b[39m\n",
"\u001b[36my\u001b[39m: \u001b[32mFloat\u001b[39m = \u001b[32m9.8765434E8F\u001b[39m\n",
"\u001b[36mface\u001b[39m: \u001b[32mChar\u001b[39m = \u001b[32m'\\u263a'\u001b[39m\n",
"\u001b[36mnumber\u001b[39m: \u001b[32mInt\u001b[39m = \u001b[32m9786\u001b[39m"
]
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"source": [
"val x: Long = 987654321\n",
"val y: Float = x // 9.8765434E8 (note that some precision is lost in this case)\n",
"\n",
"val face: Char = '☺'\n",
"val number: Int = face // 9786"
]
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"source": [
"Casting is unidirectional. This will not compile:"
]
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"name": "stderr",
"output_type": "stream",
"text": [
"cmd2.sc:3: type mismatch;\n",
" found : Float\n",
" required: Long\n",
"val z: Long = y // Does not conform\n",
" ^Compilation Failed"
]
},
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"ename": "",
"evalue": "",
"output_type": "error",
"traceback": [
"Compilation Failed"
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"source": [
"val x: Long = 987654321\n",
"val y: Float = x // 9.8765434E8\n",
"val z: Long = y // Does not conform"
]
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"source": [
"You can also cast a reference type to a subtype. This will be covered later in the tour.\n",
"\n",
"## Nothing and Null\n",
"`Nothing` is a subtype of all types, also called the bottom type. There is no value that has type `Nothing`. A common use is to signal non-termination such as a thrown exception, program exit, or an infinite loop (i.e., it is the type of an expression which does not evaluate to a value, or a method that does not return normally).\n",
"\n",
"`Null` is a subtype of all reference types (i.e. any subtype of AnyRef). It has a single value identified by the keyword literal `null`. `Null` is provided mostly for interoperability with other JVM languages and should almost never be used in Scala code. We'll cover alternatives to `null` later in the tour.\n",
"\n",
"\n",
"Tour of Scala
\n", "" ] } ], "metadata": { "kernelspec": { "display_name": "Scala (2.13)", "language": "scala", "name": "scala213" }, "language_info": { "codemirror_mode": "text/x-scala", "file_extension": ".scala", "mimetype": "text/x-scala", "name": "scala", "nbconvert_exporter": "script", "version": "2.13.1" } }, "nbformat": 4, "nbformat_minor": 4 }