Add a variable to a class instance at runtime: Difference between revisions
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"class << e" uses the ''singleton class'' of "e", which is an automatic subclass of Empty that has only this single instance. Therefore we added the "foo" accessor only to "e", not to other instances of Empty. |
"class << e" uses the ''singleton class'' of "e", which is an automatic subclass of Empty that has only this single instance. Therefore we added the "foo" accessor only to "e", not to other instances of Empty. |
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{{works with|Scala|2.10}} |
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Since version 2.10 Scala supports dynamic types. Dynamic types have to implement trait ''Dynamic'' and implement methods ''selectDynamic'' and ''updateDynamic''. |
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<lang scala>import language.dynamics |
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import scala.collection.mutable.HashMap |
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class A extends Dynamic { |
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private val map = new HashMap[String, Any] |
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def selectDynamic(name: String): Any = { |
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return map(name) |
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} |
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def updateDynamic(name:String)(value: Any) = { |
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map(name) = value |
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} |
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}</lang> |
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Sample output in the REPL: |
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<lang scala>scala> val a = new A |
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a: A = A@7b20f29d |
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scala> a.foo = 42 |
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a.foo: Any = 42 |
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scala> a.foo |
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res10: Any = 42</lang> |
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=={{header|Slate}}== |
=={{header|Slate}}== |
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{{omit from|PureBasic}} |
{{omit from|PureBasic}} |
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{{omit from|R}} |
{{omit from|R}} |
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{{omit from|TI-83 BASIC}} {{omit from|TI-89 BASIC}} <!-- Does not have objects. --> |
{{omit from|TI-83 BASIC}} {{omit from|TI-89 BASIC}} <!-- Does not have objects. --> |
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{{omit from|Retro}} |
{{omit from|Retro}} |
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