Void - Revision history

Hzwakenberg: /* A definition of Void */

2018-08-30T20:55:45Z

A definition of Void

← Older revision		Revision as of 22:55, 30 August 2018
Line 1:		Line 1:
	==A definition of <TT>Void</TT>==		==A definition of <TT>Void</TT>==

−	The <TT>Void</TT> notation corresponds to an expression having no particular type. It is used to indicate the lack of an object.	+	The <TT>Void</TT> notation corresponds to an expression having no particular type. It is used to indicate the <b>lack of an object</b>.
	<TT>Void</TT> is an elementary predefined and unmodifiable notation.		<TT>Void</TT> is an elementary predefined and unmodifiable notation.
	<TT>Void</TT> can be used like this:		<TT>Void</TT> can be used like this:

Hzwakenberg: /* Current is never Void! */

2014-09-09T12:01:10Z

Current is never Void!

← Older revision		Revision as of 14:01, 9 September 2014
Line 41:		Line 41:
	==<TT>Current</TT> is never <TT>Void</TT>!==		==<TT>Current</TT> is never <TT>Void</TT>!==
	From the principle of object-oriented programming itself,		From the principle of object-oriented programming itself,
−	[[Current\|<TT>Current</TT>]] always points to an ~~objet~~.	+	[[Current\|<TT>Current</TT>]] always points to an object.
	Comparing <TT>Current</TT> with <TT>Void</TT> has no meaning and such a		Comparing <TT>Current</TT> with <TT>Void</TT> has no meaning and such a
	comparison is also forbidden.		comparison is also forbidden.

Hzwakenberg at 17:53, 5 September 2014

2014-09-05T17:53:31Z

← Older revision		Revision as of 19:53, 5 September 2014
Line 1:		Line 1:
−	[[Category:Smarteiffel]]
−
	==A definition of <TT>Void</TT>==		==A definition of <TT>Void</TT>==

Ramack at 21:16, 4 March 2013

2013-03-04T21:16:19Z

← Older revision		Revision as of 23:16, 4 March 2013
Line 1:		Line 1:
−	[[Category:~~Book~~]]	+	[[Category:Smarteiffel]]

	==A definition of <TT>Void</TT>==		==A definition of <TT>Void</TT>==

Ramack: 11 revisions: initial import from SamrtEiffel Wiki - The Grand SmartEiffel Book

2013-03-03T21:50:50Z

11 revisions: initial import from SamrtEiffel Wiki - The Grand SmartEiffel Book

New page

[[Category:Book]]

==A definition of <TT>Void</TT>==

The <TT>Void</TT> notation corresponds to an expression having no particular type. It is used to indicate the lack of an object.
<TT>Void</TT> is an elementary predefined and unmodifiable notation.
<TT>Void</TT> can be used like this:
if my_variable = Void then
io.put_string("There's no object :-(")
else
io.put_string("There's an object !")
end
Of course, to call a method, there must be an object.
Thus, it is more frequent to see the opposite test in many programs:
if my_variable /= Void then
my_variable.a_method
end
Graphically, the lack of an object in a variable or an attribute simply corresponds to:

[[Image:MyVariableIsVoid.png|Graphical representation of <TT>Void</TT>]]

<TT>Void</TT> can also be used on the right side of the assignment sign to voluntarily lose
the reference to an object:
my_variable := Void
Of course, after the execution of the previous line,
<TT>my_variable</TT> does not reference any object anymore.

In case of a variable which is an expanded type, the use of
<TT>Void</TT> has no meaning because such a variable always contains
an object.
Actually, remember that in the case of an expanded variable, the object
is directly stored in the variable without an intermediary pointer.
It is impossible not to have an object when using an expanded variable.
For example, the comparison between a variable of type <TT>INTEGER</TT>
and <TT>Void</TT> has no meaning because the variable necessarily points out
an INTEGER and thus can never correspond to the lack of object.
For this reason, it is forbidden to compare <TT>Void</TT> with a
variable of an expanded type.

For the same reasons, the use of <TT>Void</TT> on the right side of the
assignment sign when the left side is of an expanded type is not allowed.

==<TT>Current</TT> is never <TT>Void</TT>!==
From the principle of object-oriented programming itself,
[[Current|<TT>Current</TT>]] always points to an objet.
Comparing <TT>Current</TT> with <TT>Void</TT> has no meaning and such a
comparison is also forbidden.

Cadrian: Somewhat fixed the translation. Should be checked by a native speaker though.

2005-06-17T12:54:12Z

Somewhat fixed the translation. Should be checked by a native speaker though.

New page

[[Category:Book]]

==A definition of <TT>Void</TT>==

The <TT>Void</TT> notation corresponds to an expression having no particular type. It is used to indicate the lack of an object.
<TT>Void</TT> is an elementary predefined and unmodifiable notation.
<TT>Void</TT> can be used like this:
if my_variable = Void then
io.put_string("There's no object :-(")
else
io.put_string("There's an object !")
end
Of course, to call a method, there must be an object.
Thus, it is more frequent to see the opposite test in many programs:
if my_variable /= Void then
my_variable.a_method
end
Graphically, the lack of an object in a variable or an attribute simply corresponds to:

[[Image:MyVariableIsVoid.png|Graphical representation of <TT>Void</TT>]]

<TT>Void</TT> can also be used on the right side of the assignment sign to voluntarily lose
the reference to an object:
my_variable := Void
Of course, after the execution of the previous line,
<TT>my_variable</TT> does not reference any object anymore.

In case of a variable which is an expanded type, the use of
<TT>Void</TT> has no meaning because such a variable always contains
an object.
Actually, remember that in the case of an expanded variable, the object
is directly stored in the variable without an intermediary pointer.
It is impossible not to have an object when using an expanded variable.
For example, the comparison between a variable of type <TT>INTEGER</TT>
and <TT>Void</TT> has no meaning because the variable necessarily points out
an INTEGER and thus can never correspond to the lack of object.
For this reason, it is forbidden to compare <TT>Void</TT> with a
variable of an expanded type.

For the same reasons, the use of <TT>Void</TT> on the right side of the
assignment sign when the left side is of an expanded type is not allowed.

==<TT>Current</TT> is never <TT>Void</TT>!==
From the principle of object-oriented programming itself, <TT>Current</TT> always
points to an objet.
Comparing <TT>Current</TT> with <TT>Void</TT> has no meaning and such a
comparison is also forbidden.