Extending a String

Monkey Forums/Monkey Programming/Extending a String

PoliteProgrammer

(Posted 2013) [#1]

Is it possible to extend a basic type, such as a string? I'm imagining doing something like this:

Class DerivedString Extends String
  ' Override for String.Trim()
  Method Trim:Void()
    ' ...
  End
End

This gives an error 'expecting identifier' when I try it. Basically, I'm wondering if it's possible to override some of the existing methods or add additional functionality to the basic types.

I'm aware that I can just do something like this:

Class myString
  Field str:String
  Method Trim()
  End
End

but an approach based on inheritance seems far cleaner for my purposes.

muddy_shoes

(Posted 2013) [#2]

Monkey's string type isn't really a class so you can't extend it.

ImmutableOctet(SKNG)

(Posted 2013) [#3]

Monkey's string implementation is platform specific. However, 'StringObject' could work:

'StringObject' can be found in the 'Monkey.Boxes' module. Since it's a normal Monkey-based class, it's 'passed by reference'; in other words, Monkey uses pointers (For C++ based targets anyway, most of the other targets just use their 'fake'/automated reference systems(Which use pointers anyway)). I added a 'Clone' method, just in case you ever need a clone of it.

' Here's a basic 'uppercase' String class:
Class UString Extends StringObject
	' Constructor(s):
	Method New(S:String)
		Super.New(S.ToUpper())
	End
	
	' This isn't necessary for most situations, the first constructor should work just fine.
	Method New(S:StringObject)
		Super.New(S.ToString().ToUpper())
	End
	
	' Methods:
	Method Clone:UString()
		Return New UString(Self)
	End
	
	Method Equals:Bool(Box:StringObject)
		If (Box.value.ToUpper() = value.ToUpper()) Then
			Return True
		Endif
	
		Return False
	End
	
	Method Compare:Bool(Box:StringObject)
		Return value.ToUpper().Compare(Box.value.ToUpper())
	End

	Method Output:Void()
		Print(Self.value)
	
		Return
	End
	
	' Fields:
	' Nothing so far.
End

Example:

Function Main:Int()
	Local Message:UString = "Hello world."
	
	Print("Output method:")
	Message.Output()
	
	Print("Just using the 'Print' command: ")
	Print(Message)

	Return 0
End

Console output:

Output method:
HELLO WORLD.
Just using the 'Print' command:
Hello world.

For some reason, Monkey mostly treats 'StringObject' the same way as 'String', so this would be more effective than a custom class that holds a 'String'.

The only other way is to use a custom class, or to use 'Extern', which would be problematic for some targets.