The Ring programming language version 1.10 book - Part 85 of 212

1. CHAPTER
SEVENTY
SCOPE RULES FOR VARIABLES AND ATTRIBUTES
In this chapter we will learn about scope rules and how Ring find variables.
Also we will learn about conflicts and how to solve/avoid them.
The next information are important once you start developing large applications using Ring
These application may uses
• Global variables (Try to avoid them)
• Classes (Object-Oriented)
• braces { } to access objects
• Declarative Programming
• Natural Programming
70.1 Three Scopes
In Ring we have three scopes :-
1. Public/Global Scope - Each variable you define in the statements part (before functions and classes)
2. Object Scope - When you are inside an object (Inside class method or using { } to access the object )
3. Local Scope - Related to functions and methods
70.2 Defining Variables and Variables Access
1. Ring uses lexical scoping, i.e. the scope of the variable is based on where we defined the variable.
2. Inside braces { } when you access an object, You will change the current active object scope to this object scope
but you still can access the global scope and the local scope.
3. After the ‘Class’ keyword and the class name, when you write variable names to be defined as attributes, You
still can access the global scope.
In this region (class region - after the class name and before methods) we have
• Global Scope —-> The Global Scope
• Object Scope —-> The Object Scope
• Local Scope —-> The Object Scope
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Note: Since the local scope in the class region point also to the object scope in this region, we can use nested braces
and still have access to the object scope of the class through the local scope.
Tip: You can create windows and controls as attibutes by defining them in this region.
Tip: In the class region if you created objects and used braces {} to access them then using self.attribute inside braces
will use the class (not the object that you access) because you have access to the class through the local scope.
4. Function Parameters are automatically defined in the local scope.
70.3 How Ring find the variable?
1 - Search First in the Local Scope
if not found !
2 - Search in the Object Scope
if not found !
3 - Search in the public scope
if not found —-> Runtime Error
if found —-> Check if we can do optimization to avoid searching next time (Cache / Pointers for performance).
70.4 Using Object.Attribute
When we use object.attribute the search will be in the object attributes only.
I.e. no search will be done in the local scope or in the global scope for the object attribute.
Note: Using self.attribute will search for the first self before searching for attributes.
70.5 The Self Object
The self object is a reference to the current object that we can use from the class methods.
When we are inside class method and use Self we mean the object that will be created from this class.
Inside the class methods if we used Braces { } this will change the current object scope and self will be changed also
inside braces to reference the object that we access using Braces.
Inside the Class Region (after the class name and before any method) we have access to the object through the object
scope and the local scope also. In this region using Self will always be a reference to the class object. if we used
Braces to change the object scope then used Self inside Braces, Also self will be a reference to the class object (not
the object that we already access using braces) because in the class region we have :-
• Global Scope —> Global Scope
• Object Scope —> Object Scope
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• Local Scope —> Object Scope
And using Braces changes the object scope only (not the local scope) and when Ring search for variables it will search
in the Local Scope first so it will find self in the class that we are inside.
70.6 How Ring Define Variables and Attributes
Ring will use the variable name in the Assignment operation
1 - Search using the variable name
2 - If not found —> Avoid the runtime error and define the variable in the current scope
3 - If found —> Use the variable and don’t define anything in the current scope
• In the global region (before any function or class) the current scope is the global scope.
• In the class region (after the class name and before any method) the current scope is the object attributes.
• In Functions and methods the current scope is the local scope.
70.7 Conflict between Global Variables and Class Attributes
Look at this example:
name = "test"
o1 = new person
see o1
class person
name
address
phone
In the previous example we have a global variable called ‘name’ inside the class person.
when we use the variable ‘name’, Ring will start the search operation and will try to find it.
if found —> Use it
if not found —> Define new attribute
But the variable name is a global variable, so it will be found and used!
We will not have the attribute name! added to the object.
Solution (1) - Use the Main Function
func main
name = "test"
o1 = new person
see o1
class person
name
address
phone
Solution (2) - Use special mark for global variable names like $
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$name = "test"
o1 = new person
see o1
class person
name
address
phone
Solution (3) - Use the AddAttribute() Method
name = "test"
o1 = new person
see o1
class person
AddAttribute(self,"name")
address
phone
Solution (4) - Use self before the attribute name
name = "test"
o1 = new person
see o1
class person
self.name
address
phone
So what is the best solution to this conflict?
1 - Use the $ Mark for global variables
2 - Optional : Try to avoid global variables and use the Main function
In practice i do both of them.
The other solution
• Use self before the attribute name or use AddAttribute()
70.8 Conflict between Class Attributes and Local Variables
This conflict may happen when we access the object using braces
Example:
func main
name = "nice"
o1 = new person {name="mahmoud" address="Egypt" phone = 000 }
see o1
class person
name
address
phone
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In the previous example we have the local variable name.
The value of this variable will be set to “mahmoud” instead of the object attribute.
Solution (1) : Just use Self
func main
name = "nice"
o1 = new person {self.name="mahmoud" address="Egypt" phone = 000 }
see o1
class person
name
address
phone
Solution (2) : Change the Local variable name
func main
cName = "nice"
o1 = new person {name="mahmoud" address="Egypt" phone = 000 }
see o1
class person
name
address
phone
Solution (3) : Change Braces and use the Dot operator
func main
name = "nice"
o1 = new person
o1.name ="mahmoud"
o1.address ="Egypt"
o1.phone = 000
see o1
class person
name
address
phone
70.9 Using Braces to access objects inside Class Methods
Remember that we have Three scopes (Local Scope, Object Scope and Global Scope) and when we are inside a class
method, we expect that we have access to the object attributes and methods and this is true until we use braces to
access another object attributes and methods because in this case our object scope will be switched to another object.
new point { test() }
class point
x=10 y=20
func test
see x + nl + y + nl # works fine
myobj = new otherclass {
see name + nl
see x + nl + y + nl # error !
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}
class otherclass
name = "test"
Output:
10
20
test
Line 8 Error (R24) : Using uninitialized variable : x
In method test() in file methodbraceerror.ring
called from line 5 in file methodbraceerror.ring
Now what we will do to solve the previous problem?
Solution (1) : Write the code that access the class attributes outside braces.
new point { test() }
class point
x=10 y=20
func test
see x + nl + y + nl # works fine
myobj = new otherclass {
see name + nl
}
see x + nl + y + nl # Outside braces - works fine
class otherclass
name = "test"
Output:
10
20
test
10
20
Solution (2) : Don’t Use Braces
new point { test() }
class point
x=10 y=20
func test
see x + nl + y + nl
myobj = new otherclass
see myobj.name
see x + nl + y + nl
class otherclass
name = "test"
Solution (3) : Copy the self object
We may use this solution if we want to use braces and get access to the class attributes (Just Reading).
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new point { test() }
class point
x=10 y=20
func test
oSelf = self
see x + nl + y + nl
myobj = new otherclass {
see name + nl
see oself.x + nl + oself.y + nl
}
class otherclass
name = "test"
Output:
10
20
test
10
20
Now look at this line
oself = self
The problem with the previous line is that we will have a new copy from the object Because in Ring the assignment
operator copy lists and objects by value (not by reference).
When we access the new object attributes (reading) we don’t have problems
But if we modified the object attributes (Then we will modify the copy!).
Note: We can use braces again with the copy
new point { test() }
class point
x=10 y=20
func test
oSelf = self
see x + nl + y + nl
myobj = new otherclass {
see name + nl
oSelf {
see x + nl + y + nl
}
}
class otherclass
name = "test"
In a GUI application, we may create a class contains the window objects as attributes to be able to access the controls
from different methods. Remember the previous information when you try to access objects using braces inside
methods because in this case you can’t access the object attributes directly and if you copied the self object you will
work on a copy and the new controls that you create will be related to the copy and you can’t access them.
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70.10 Accessing the class attributes from braces inside class meth-
ods
We access the class attributes directly from the class methods, also we have the choice to use the Self reference before
the attribute/method name. Using Braces {} inside class method change the active object scope and prevent us from
getting direct access to the class attributes. Also using Self will not help because the Self reference will be changed to
the object that we access using Braces.
In this case if you want to read an attribute you have to copy the Self object before using Braces and if you want to
modify an attribute you have to the copy from local variable to the object attribute after using Braces.
This case happens when you want to read/modify attribute insead braces.
Class MyApp
oCon # Attribute
# some code here
Func OpenDatabase
# some code here
new QSqlDatabase() {
oCon = addDatabase("QSQLITE") {
setDatabaseName("weighthistory.db")
open()
}
}
self.oCon = oCon
# some code here
In the previous example we want to create the connection object and save it inside the oCon attribute.
The object is an output from the addDatabase() method that we use after accessing the QSQLDatabase() object.
Inside braces we can’t use the Self reference to use the object created from the MyApp class, Because the Self reference
here will be to the object that we access using Braces.
We solved the problem in the previous example by creating a local variable called oCon then after Braces we copied
that variable to the oCon attribute.
The next code is another solution.
Class MyApp
oCon # Attribute
# some code here
Func OpenDatabase
# some code here
oCon = new QSqlDatabase()
oCon = oCon.addDatabase("QSQLITE") {
setDatabaseName("weighthistory.db")
Open()
}
# some code here
The next code is a better solution.
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Class MyApp
oCon # Attribute
# some code here
Func OpenDatabase
# some code here
new QSqlDatabase() {
this.oCon = addDatabase("QSQLITE") {
setDatabaseName("weighthistory.db")
Open()
}
}
# some code here
Note: We used this.attribute to access the class attribute (oCon) while we are inside Braces.
70.11 Creating a Class for each Window in GUI applications
A good way for creating classes for windows is to define the window directly after the class name
In this area you can use nested braces without problems to define the window and the controls, and they will be
attributes that you can access from methods.
Example:
Load "guilib.ring"
new qApp
{
$ObjectName = "oFirstWindow"
oFirstWindow = new FirstWindow
$ObjectName = "oSecondWindow"
oSecondWindow = new SecondWindow
exec()
}
Class FirstWindow
win = new qWidget() {
setgeometry(0,50,300,200)
setWindowTitle("First Window")
label1 = new qLabel(win)
{
setgeometry(10,10,300,30)
setText("0")
}
btn1 = new qPushButton(win)
{
move(100,100)
setText("Increment")
setClickEvent($ObjectName+".increment()")
}
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show()
}
Func Increment
label1 {
setText( "" + ( 0 + text() + 1 ) )
}
Class SecondWindow
win = new qWidget() {
setgeometry(400,50,300,200)
setWindowTitle("Second Window")
label1 = new qLabel(win)
{
setgeometry(10,10,300,30)
setText("0")
}
btn1 = new qPushButton(win)
{
move(100,100)
setText("Decrement")
setClickEvent($ObjectName+".decrement()")
}
show()
}
Func Decrement
label1 {
setText( "" + ( 0 + text() - 1 ) )
}
70.12 Conflict between self inside braces and self in the class region
In the class region (after the class name and before any methods) we define the attributes.
In this region we have access to the global scope and the local scope will point to the object scope.
Three Scopes
• Global Scope —> Gloabl Scope
• Object Scope —> Object Scope
• Local Scope —> Object Scope
Look at this example
New Account {
see aFriends
}
Class Account
name = "Mahmoud"
aFriends = []
aFriends + new Friend {
name = "Gal"
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