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Literals

A literal denotes a fixed, unchangeable value. Literals for strings, numbers, booleans, null, and Java types are supported, as well as literals for unmodifiable collection types like lists, sets, maps, and arrays.

1. String Literals

A string literal is of type String. String literals are enclosed in a pair of single quotes or double quotes. Special characters can be quoted with a backslash or defined using unicode notation.

var a = 'Hello World!'
var b = "Hello World!"
var c = 'Hello "World!"'
var d = "Hello "World!""
var e = "Hello 
            World!"

Unlike Java, SARL strings can span multiple lines, as ilustrated by the variable e above.

2. Character Literals

Character literals use the same notation as String literals. If a single-character String literal is used in a context where a primitive char or the wrapper type Character or char is expected, the compiler will treat the literal as a Character or char value.

var a : char = 'a'
var b : char = "b"

3. Number Literals

3.1. General Notation

SARL supports the same number literals as Java with two exceptions: there is no notation for specifying octal numbers, and if you put the dot character in a number, you must specify both the integer and fractional parts.

var a = 42      // Decimal
var b = 0xbeef  // Hexadecimal
var c = 077     // Decimal 77, NOT octal
var d = 0.1     // The leading zero must be specified
var e = 1.0     // The trailing zero must be specified
Type of Integer Description Example
Hexadecimal Prefix is 0x 0xbeef
Octal Not supported
Decimal No prefix, no fractional part 077
Rational No prefix, fractional part 0.1

3.2. Integer suffixes

Post-fixing an integer literal may change its type:

Examples:

var anInteger = 1234

var aLong = 1234L

var aBigInteger = 1234bi

4. Floating-point-value suffixes

Post-fixing a floating-point literal may change its type:

Examples:

var aDouble = 1234.0

var anotherDouble = 5678d

var aFloat = 1234.0f

var anotherFloat = 5678f

var aBigDecimal = 1234bd

4.1. Large Numbers

As in Java 7, you can separate digits using _ for better readability of large numbers.

// underscore is ignored, L for long
var a = 12_345_678L

5. Boolean Literals

There are two boolean literals, true and false, which correspond to their Java counterpart of type boolean.

6. Null Literal

The null pointer literal null has exactly the same semantics as in Java: a reference to nothing.

7. Type Literals

A type literal is the fully qualified name of a type in the SARL language. The syntax for type literals is generally the plain name of the type. Nested types use the delimiter .. The following example is the type literal for the Agent type.

io.sarl.lang.core.Agent

To disambiguate the type expression with the . operator for invoking a function, the type literal may also be specified using the typeof operator.

typeof(io.sarl.lang.core.Agent)

Consequently, it is possible to access the members of a type reflectively by using its plain name. In the following example, the fields declared in the String class are provided:

String.getDeclaredFields

8. Collection Literals

The collection literals permit to specify collections of values.

8.1. Mutable Collections

It is easy to create instances of collections since the methods in CollectionLiterals are automatically imported. They permit you to create instances of collections from the JDK.

interface CollectionLiterals {
    def emptyList : List<Object>
    def emptyMap : Map<Object, Object>
    def emptySet : Set<Object>
    def newArrayList : ArrayList<Object>
    def newArrayList(Object[]*) : ArrayList<Object>
    def newHashMap : HashMap<Object, Object>
    def newHashMap(Pair<Object, Object>[]*) : HashMap<Object, Object>
    def newHashSet : HashSet<Object>
    def newHashSet(Object[]*) : HashSet<Object>
    def newImmutableList(Object[]*) : List<Object>
    def newImmutableMap(Pair<Object, Object>[]*) : Map<Object, Object>
    def newImmutableSet(Object[]*) : Set<Object>
    def newLinkedHashMap : LinkedHashMap<Object, Object>
    def newLinkedHashMap(Pair<Object, Object>[]*) : LinkedHashMap<Object, Object>
    def newLinkedHashSet : LinkedHashSet<Object>
    def newLinkedHashSet(Object[]*) : LinkedHashSet<Object>
    def newLinkedList : LinkedList<Object>
    def newLinkedList(Object[]*) : LinkedList<Object>
    def newTreeMap(Comparator<Object>) : TreeMap<Object, Object>
    def newTreeMap(Comparator<Object>, Pair<Object, Object>[]) : TreeMap<Object, Object>
    def newTreeSet(Comparator<Object>) : TreeSet<Object>
    def newTreeSet(Comparator<Object>, Object[]) : TreeSet<Object>
}

In the following example, an array-based list with two strings of characters and a linked hash map with two pairs are created.

var myList = newArrayList('Hello', 'world')
var myMap = newLinkedHashMap('a' -> 1, 'b' -> 2)

8.2. Array Literals

Java arrays can be created either using a literal as described in the next section, or a new array with a fixed size.

Array Creation

The methods from ArrayLiterals are automatically included.

interface ArrayLiterals {
    def newArrayOfSize(int) : Object[]
    def newBooleanArrayOfSize(int) : boolean[]
    def newByteArrayOfSize(int) : byte[]
    def newCharArrayOfSize(int) : char[]
    def newDoubleArrayOfSize(int) : double[]
    def newFloatArrayOfSize(int) : float[]
    def newIntArrayOfSize(int) : int[]
    def newLongArrayOfSize(int) : long[]
    def newShortArrayOfSize(int) : short[]
}

This utility class provides a collection of methods, such as `ArrayLiterals.newArrayOfSize(int)` for creating array literals.

// variable a contains a array of size 400 which contains Objects.
var a : String[] = newArrayOfSize(400)
// variable b contains a array of size 200 which contains int values.
var b : int[] = newIntArrayOfSize(200)

Array Element Accessors

Retrieving and setting values of arrays is done through the extension methods get(int) and set(int, T). The first parameter of these two functions are the position of the element to get or set. As with Java, the index of the elements in the array starts with 0. The second parameter of set is the value to put at the specified position in the array.

The method length is available for retrieving the size of the array.

var a = #['Hello', 'world', '!']

// variable b contains the second element of the array a: 'world'.
var b = a.get(1)

// change the first element in the array a.
a.set(0, 'New Element')

// variable c contains the size of the array a: 3.
var c = a.length

Array to List

Arrays are automatically converted to lists when needed. This is similar to the boxing and unboxing features provided by Java to convert between the primitives and their respective object types. This convertion is not done by copying the elements of array. The [Facade design pattern] is used for creating a specific List implementation that uses the original array as its internal backed data structure. This method is similar to the Arrays.asList function provided by the Java API.

In the following example, an array is defined and converted to a list.

val myArray : int[] = #[1,2,3]
val myList : List<Integer> = myArray

8.3. Immutable Collections

In addition to the functions described in the previous section, SARL supports collection literals to create immutable collections and arrays, depending on the target type. There are three types of immutable collections: array, set, and hash table.

An immutable array of values is specified with the #[ and ] delimiters.

var a = #[ 'Hello', 'World' ]

An immutable set of values is specified with the #{ and } delimiters.

var b = #{ 'Hello', 'World' }

An immutable map of pairs is specified with the #{ and } delimiters, as for immutable sets, but the values are pairs, using the ->.

var c = #{ 'a' -> 1 ,'b' -> 2 }

9. Acknowledgements

This documentation is inspired by the documentations from the Xtext and Xtend projects.

Copyright © 2014-2018 the original authors or authors.

Licensed under the Apache License, Version 2.0; you may not use this file except in compliance with the License. You may obtain a copy of the License.

You are free to reproduce the content of this page on copyleft websites such as Wikipedia.

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