Respond to an unknown method call: Difference between revisions

Content added Content deleted
(added Fantom example)
(updated Fantom solution to trap only unknown methods)
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=={{header|Fantom}}==
=={{header|Fantom}}==


In Fantom, you can call methods statically or dynamically. Static calls to methods will be checked at compile time. Dynamic method calls (indicated by an <code>instance->method</code> syntax) are run through a "[http://fantom.org/doc/sys/Obj.html#trap trap]" method at run time, and can thus be caught:
In Fantom, you can call methods statically or dynamically. Static calls to methods will be checked at compile time. Dynamic method calls (indicated by an <code>instance->method</code> syntax) are run through a "[http://fantom.org/doc/sys/Obj.html#trap trap]" method at run time. This method looks up the given method name, and throws an exception if the method/field is not known. This exception can be caught, and processed specially:


<lang fantom>
<lang fantom>
class A
class A
{
{
public Void doit (Int n)
{
echo ("known function called on $n")
}

// override the 'trap' method, which catches dynamic invocations of methods
// override the 'trap' method, which catches dynamic invocations of methods
override Obj? trap(Str name, Obj?[]? args := null)
override Obj? trap(Str name, Obj?[]? args := null)
{
{
try
⚫
echo ("In trap, you called: " + name + " with args " + args.join(","))
return null
{
return super.trap(name, args)
}
catch (UnknownSlotErr err)
{
⚫
echo ("In trap, you called: " + name + " with args " + args.join(","))
return null
}
}
}
}
}
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a := A()
a := A()
// note the dynamic dispatch
// note the dynamic dispatch
a->doit (1)
a->methodName (1, 2, 3)
a->methodName (1, 2, 3)
}
}
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<pre>
<pre>
$ fan unknown-method.fan
$ fan unknown-method.fan
known function called on 1
In trap, you called: methodName with args 1,2,3
In trap, you called: methodName with args 1,2,3
</pre>
</pre>

In normal usage, the trap method tries to locate the named method using reflection on the current class.


=={{header|J}}==
=={{header|J}}==
Retrieved from "https://rosettacode.org/wiki/Respond_to_an_unknown_method_call"