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Delegates: Difference between revisions
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=={{header|zkl}}==
{{trans|Scala}}
<lang zkl>class Thingable{ var thing; }
class Delegator{
var delegate;
fcn operation{
if (delegate) delegate.thing;
else "default implementation"
}
}
class Delegate(Thingable){ thing = "delegate implementation" }</lang>
<lang zkl> // Without a delegate:
a:= Delegator();
a.operation().println(); //--> "default implementation"
// With a delegate:
a.delegate = Delegate();
a.operation().println(); //-->"delegate implementation"</lang>
A second example
<lang zkl>class [static] Logger{ // Only one logging resource
var [mixin=File] dst; // File like semantics, eg Data, Pipe
dst = File.DevNull;
// initially, the logger does nothing
fcn log(msg){dst.writeln(vm.pasteArgs())}
}</lang>
<lang zkl>Logger.log("this is a test"); //-->nada
Logger.dst=Console;
Logger.log("this is a test 2"); //-->writes to Console
class B(Logger){ log("Hello from ",self,"'s constructor"); }
B(); //-->Hello from Class(B)'s constructor</lang>
The base class B was constructed at startup,
so the first Hello went to DevNull as all base classes are created before
code runs (base classes are used to create class instances, eg B()).
{{Omit From|ALGOL 68}} <!-- it isn't immediately obvious that ALGOL 68 is object oriented -->
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