Best way to detect class of variable

Monkey Forums/Monkey Programming/Best way to detect class of variable

Shagwana

(Posted 2013) [#1]

Consider the following snippet of code...

Class base
End Class

Class foo Extends base
End Class

Class bar Extends base
	Field sText:String="working as expected"
End Class


Function Main()

	'Working as expected
	Local a:base = New bar
	Print bar(a).sText
	
	'Causes Error at runtime (correct)
	Local b:base = New foo
	Print bar(b).sText	
	
End Function

If you run the above code you will see it print...

working as expected
Monkey Runtime Error : Null object access

This is correct and expected.

My question is, what is good way of detecting if variable 'b' is indeed of class bar?.

So that I know not to run 'Print bar(b).sText'.

Shagwana

(Posted 2013) [#2]

One solution I have is this...


Class base
	
	Method ClassType:Int() Abstract

	Const iTYPE_FOO:Int = 1
	Const iTYPE_BAR:Int = 2

End Class

Class foo Extends base

	Method ClassType:Int()
		Return base.iTYPE_FOO
	End Method

End Class

Class bar Extends base

	Method ClassType:Int()
		Return base.iTYPE_BAR
	End Method

	Field sText:String="working as expected"
End Class


Function Main()

	'Working as expected
	Local a:base = New bar
	Print bar(a).sText
	
	'Causes Error at runtime (correct)
	Local b:base = New foo
	If b.ClassType() = base.iTYPE_BAR
		Print bar(b).sText	
	Endif
	
End Function

Now this is not ideal as it means implementing a method that I would rather not have in each of the extended classes. Also means looking after a list of constants as well.

Feature request: If we could abstract Constants then we would be able to do the above much simpler!.

Shagwana

(Posted 2013) [#3]

Figured it out...


Class base	
End Class

Class foo Extends base
End Class

Class bar Extends base 
	Field sText:String="working as expected"
End Class



Function Main()

	'Working as expected
	Local a:base = New bar
	Print bar(a).sText
	
	'Causes Error at runtime (correct)
	Local b:base = New foo
	If bar(b) <> null
		Print bar(b).sText	
	Endif
	
End Function

And that is the solution I was looking for!.