Polymorphic copy: Difference between revisions
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This example handles dictionaries (and anything that implements a sufficiently dictionary like interface to support the ''items()'' method along with the ''__setitem__()'' method. (statements of the form '''''x[y] = z''''' in Python are implicitly calling the ''__setitem__()'' method of the "x" object, passing it a key of "y" and a value of "z." Similarly this code tests if an item is a sequence (one can call the "len()" built-in function on it) and, if so, uses a slice assignment to perform a shallow copy. For any other type of object a simple binding is performed. Technically this last case will not "copy" anything ... it will create a new name binding to the object to which "source" was already a reference. The earlier binding of a "blank" instance of the source's __class__ will be replaced. So the trick of creating the blank object of the same type is only meaningful for the other types. In the cases of strings, integers and other numbers the objects themselves are immutable and the bindings are all dynamic (so the entire task is moot with respect to them). |
This example handles dictionaries (and anything that implements a sufficiently dictionary like interface to support the ''items()'' method along with the ''__setitem__()'' method. (statements of the form '''''x[y] = z''''' in Python are implicitly calling the ''__setitem__()'' method of the "x" object, passing it a key of "y" and a value of "z." Similarly this code tests if an item is a sequence (one can call the "len()" built-in function on it) and, if so, uses a slice assignment to perform a shallow copy. For any other type of object a simple binding is performed. Technically this last case will not "copy" anything ... it will create a new name binding to the object to which "source" was already a reference. The earlier binding of a "blank" instance of the source's __class__ will be replaced. So the trick of creating the blank object of the same type is only meaningful for the other types. In the cases of strings, integers and other numbers the objects themselves are immutable and the bindings are all dynamic (so the entire task is moot with respect to them). |
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=={{header|Ruby}}== |
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All Ruby objects inherit two methods for copying themselves: "clone" and "dup". I don't really understand the difference between them. |
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<ruby>class T |
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def name |
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"T" |
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end |
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end |
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class S |
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def name |
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"S" |
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end |
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end |
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obj1 = T.new |
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obj2 = S.new |
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print obj1.dup.name # prints "T" |
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print obj2.dup.name # prints "S"</ruby> |
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