mirrors/eiffel-org
1
0
Fork 0
mirror of https://github.com/EiffelSoftware/eiffel-org.git synced 2025-12-07 07:12:25 +01:00
Code Issues Packages Projects Releases Wiki Activity

Author:halw

Browse Source 
Date:2011-09-17T23:25:22.000000Z


git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@976 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
This commit is contained in:
halw
2011-09-17 23:25:22 +00:00
parent 2930e4f44b
commit 6fc9a28f22
2 changed files with 66 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
documentation/current/method/eiffel-tutorial-et/et-instructions.wiki
View File

@@ -29,7 +29,7 @@ The rule that governs validity of assignments expands upon this and is generaliz
The phrase "'''compatible with'''" in this rule means that either it "'''conforms to'''" or "'''converts to'''".
We saw conformance defined in the section on [[ET: Inheritance#polymorphism|polymorphism]]. [[ET: Other Mechanisms#Convertibility|Convertibility]] is explained in the section on [[ET: Other Mechanisms#Convertibility|Other Mechanisms]].
We saw conformance defined in the section on [[ET: Inheritance#polymorphism|Polymorphism]]. [[ET: Other Mechanisms#Convertibility|Convertibility]] is explained in the section on [[ET: Other Mechanisms#Convertibility|Other Mechanisms]].
===Conditional===

70
documentation/current/method/eiffel-tutorial-et/et-other-mechanisms.wiki
View File

@@ -138,8 +138,6 @@ The validity of a non-object call is restricted in ways that mirror these primar
==Convertibility==
{{underconstruction}}
It is useful at times to designate the instances of one type can be created through conversion of instance of some other type. This can be done through an Eiffel mechanism called '''convertibility'''.
{{Definition|Convertibility: converts to, converts from|<br/>
@@ -170,11 +168,73 @@ Let's look at an example that may already be familiar to you.
In the snippet above, we have attributes declared of type <code>STRING</code> and <code>SYSTEM_STRING</code>.
We know that if we have a attribute of type <code>STRING</code> that we can make a direct assignment of a .Net type of string (that is, the .Net type <code>System.String</code> which we see as class SYSTEM_STRING) to our STRING attribute.
We know that if we have a attribute of type <code>STRING</code> that we can make a direct assignment of a .Net type of string (that is, the .Net type <code>System.String</code> which we see as class <code>SYSTEM_STRING</code>) to our <code>STRING</code> attribute.
We know also that SYSTEM_STRING does not conform to STRING, so according to the definition of compatibility, this must happen by conversion.
We know also that <code>SYSTEM_STRING</code> does not conform to <code>STRING</code>, so according to the definition of [[ET: Instructions#Assignment and attachment|compatibility]], this must happen through conversion.
It is possible because SYSTEM_STRING converts to STRING.
Therefore <code>SYSTEM_STRING</code> converts to <code>STRING</code>. And according to the definition above this means that either:
# Class <code>SYSTEM_STRING</code> has a conversion query listing <code>STRING</code> as a conversion type, or
# Class <code>STRING</code> has a conversion procedure listing <code>SYSTEM_STRING</code> as a conversion type
In this case <code>STRING</code> has a conversion procedure for objects of type <code>SYSTEM_STRING</code>. Conversion procedures are always [[ET: The Dynamic Structure: Execution Model#Creating and initializing objects|creation procedures]]. So they appear in both the <code>create</code> and the <code>convert</code> parts of the class.
<code>
class STRING
…
create
make_from_cil
…
convert
make_from_cil ({SYSTEM_STRING})
…
</code>
We won't show the implementation of the conversion procedure, but as you can imagine, it initializes its target with the content of its argument.
Because of convertibility, this code:
<code>
my_string := my_system_string
</code>
is equivalent to:
<code>
create my_string.make_from_cil (my_system_string)
</code>
So, we've seen how <code>SYSTEM_STRING</code> converts to <code>STRING</code>. But, in the context of our example, we could also do this:
<code>
my_system_string := my_string
</code>
Which means that <code>STRING</code> converts to <code>SYSTEM_STRING</code>. The <code>convert</code> part of class <code>STRING</code> also has a conversion query listing <code>SYSTEM_STRING</code> as a conversion type:
<code>
class STRING
…
create
make_from_cil
…
convert
make_from_cil ({SYSTEM_STRING})
to_cil: {SYSTEM_STRING}
…
</code>
Because of convertibility, this code:
<code>
my_system_string := my_string
</code>
is equivalent to:
<code>
my_system_string := my_string.to_cil
</code>
==Tuple types==