Local vs local types

BlitzMax Forums/BlitzMax Beginners Area/Local vs local types

Ole JR

(Posted 2007) [#1]

Doh.. The topic should really be Global vs Local..

When I do like this I get the result I'm after:

Global a:Int = 1

Function Test()
  Local b:Int
  b = a
  b = 2
EndFunction
DebugLog a
Test()
DebugLog a

(Local b don't change the Global a)

But doing the same thing with a Type:

Type TTest
  Field x:Int
EndType

Global a:TTest = New TTest

Function Test()
  Local b:TTest = New  TTest
  b = a
  b.x = 2
EndFunction

a.x = 1
DebugLog a.x
Test()
DebugLog a.x

Why does the Local type change the global one..?

H&K	(Posted 2007) [#2]

In the second example B is a local pointer to a, (as apposed to has the value a in the first example).

So in 1)
b=A means let b have the value that a has
b=2 meand let the variable held in b = 2
This is how it works for all the normal variables (Int, Float, double etc)

in 2)
b=a means let b point to the same instance of TTest as a does
b.x = 2 means let the field pointed to by b.x = 2
This is how it works for anything extended from "Object" (Basicly all Types)

b:int = a:int > Let the variable B have the value of a
B:type = A:Type > Let the pointer b point to the same place as pointer A

This is one of the reasons that you need to write your own copy methods (Edit: Of which Perts "Clone" method is one)

Perturbatio

(Posted 2007) [#3]

because "b" becomes a reference to "a", it is not a copy of a, it simply refers to the same location.

Type TTest
	Field x:Int
	Method Clone:TTest()
		Local myClone:TTest = New TTest
			myClone.x = x
		Return myClone
	End Method
EndType

Global a:TTest = New TTest

Function Test()
  Local b:TTest = New  TTest
  b = a.Clone()
  b.x = 2
EndFunction

a.x = 1
DebugLog a.x
Test()
DebugLog a.x

Ole JR

(Posted 2007) [#4]

Just as I thought then..

Thanks for the clone tip/example.

Czar Flavius

(Posted 2007) [#5]

In your second function, the new instance of TTest you create for b is basically deleted right away and replaced with a's TTest.