forked from Mirror/wren
90 lines
2.5 KiB
Markdown
90 lines
2.5 KiB
Markdown
^title Values
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^category types
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Values are the built-in object types that all other objects are composed of.
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They can be created through *literals*, expressions that evaluate to a value.
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All values are *immutable*—once created, they do not change. The number
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`3` is always the number `3`. The string `"frozen"` can never have its
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character array modified in place.
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## Booleans
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A boolean value represents truth or falsehood. There are two boolean literals,
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`true` and `false`. Their class is [Bool](core/bool.html).
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## Numbers
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Like other scripting languages, Wren has a single numeric type:
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double-precision floating point. Number literals look like you expect coming
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from other languages:
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:::dart
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0
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1234
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-5678
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3.14159
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1.0
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-12.34
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Numbers are instances of the [Num](core/num.html) class.
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## Strings
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Strings are chunks of text stored as UTF-8. Their class is
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[String](core/string.html). String literals are surrounded in double quotes:
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:::dart
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"hi there"
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A handful of escape characters are supported:
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:::dart
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"\"" // A double quote character.
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"\\" // A backslash.
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"\a" // Alarm beep. (Who uses this?)
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"\b" // Backspace.
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"\f" // Formfeed.
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"\n" // Newline.
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"\r" // Carriage return.
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"\t" // Tab.
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"\v" // Vertical tab.
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A `\u` followed by four hex digits can be used to specify a Unicode code point.
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## Ranges
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A range is a little object that represents a consecutive range of integers.
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They don't have their own dedicated literal syntax. Instead, the number class
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implements the `..` and `...` [operators](expressions.html#operators) to create
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them:
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:::dart
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3..8
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This creates a range from three to eight, including eight itself. If you want a
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half-inclusive range, use `...`:
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:::dart
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4...6
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This creates a range from four to six *not* including six itself. Ranges are
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commonly used for [iterating](control-flow.html#for-statements) over a
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sequences of numbers, but are useful in other places too. You can pass them to
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a [list](lists.html)'s subscript operator to return a subset of the list, for
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example:
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:::dart
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var list = ["a", "b", "c", "d", "e"]
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var slice = list[1..3]
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IO.print(slice) // ["b", "c", "d"]
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Their class is [Range](core/range.html)
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## Null
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Wren has a special value `null`, which is the only instance of the class
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[Null](core/null.html). (Note the difference in case.) It functions a bit like
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`void` in some languages: it indicates the absence of a value. If you call a
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method that doesn't return anything and get its returned value, you get `null`
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back.
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