Add a variable to a class instance at runtime: Difference between revisions
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=={{header|Pop11}}== |
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In Pop11 instance variables (slots) are specified at class creation |
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time and there is no way to add new slot to an instance after its |
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class was created. However, for most practical purposes one can |
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obtain desired effect in different way. Namely, except for a few |
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low-lever routines slots in Pop11 are accessed via getter and |
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setter methods. Getters and setters are like ordinary methods, |
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but are automatically defined and "know" low level details of |
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slot access. Pop11 allows dynamic definition of methods, and |
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one can add new methods which work as "getter" and "setter" but |
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do not store data directly in instance. One possibility is |
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to have one instance variable which contains a hastable (this |
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is essentially what Perl solution is doing). Another possibility |
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(used below) is to create na external hashtable. Adding new slots |
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typically make sense if slot name is only known at runtine, so |
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we create method definition (as a list) at runtime and compile |
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it using the 'pop11_compile' procedure. |
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<pre> |
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lib objectclass; |
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define :class foo; |
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enddefine; |
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define define_named_method(method, class); |
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lvars method_str = method >< ''; |
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lvars class_str = class >< ''; |
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lvars method_hash_str = 'hash_' >< length(class_str) >< '_' |
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>< class_str >< '_' >< length(method_str) |
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>< '_' >< method_str; |
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lvars method_hash = consword(method_hash_str); |
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pop11_compile([ |
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lvars ^method_hash = newassoc([]); |
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define :method ^method(self : ^class); |
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^method_hash(self); |
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enddefine; |
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define :method updaterof ^method(val, self : ^class); |
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val -> ^method_hash(self); |
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enddefine; |
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]); |
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enddefine; |
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define_named_method("met1", "foo"); |
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lvars bar = consfoo(); |
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met1(bar) => ;;; default value -- false |
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"baz" -> met1(bar); |
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met1(bar) => ;;; new value |
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</pre> |
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=={{header|Python}}== |
=={{header|Python}}== |
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