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Author:halw

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Date:2011-09-19T03:37:05.000000Z


git-svn-id: https://svn.eiffel.com/eiffel-org/trunk@977 abb3cda0-5349-4a8f-a601-0c33ac3a8c38
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halw
2011-09-19 03:57:52 +00:00
parent 6fc9a28f22
commit 034b4b45ed
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documentation/current/method/eiffel-tutorial-et/et-other-mechanisms.wiki
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@@ -158,7 +158,7 @@ Before we get into an example of convertibility, let's list some of its underlyi
Let's look at an example that may already be familiar to you. Let's look at an example that may already be familiar to you.
<code> <code>
my_string: STRING my_string: STRING_8
my_system_string: SYSTEM_STRING my_system_string: SYSTEM_STRING
… …
@@ -166,21 +166,21 @@ Let's look at an example that may already be familiar to you.
my_string := my_system_string my_string := my_system_string
</code> </code>
In the snippet above, we have attributes declared of type <code>STRING</code> and <code>SYSTEM_STRING</code>. In the snippet above, we have attributes declared of type <code>STRING_8</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 <code>SYSTEM_STRING</code>) to our <code>STRING</code> attribute. We know that if we have a attribute of type <code>STRING_8</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_8</code> attribute.
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. We know also that <code>SYSTEM_STRING</code> does not conform to <code>STRING_8</code>, so according to the definition of [[ET: Instructions#Assignment and attachment|compatibility]], this must happen through conversion.
Therefore <code>SYSTEM_STRING</code> converts to <code>STRING</code>. And according to the definition above this means that either: Therefore <code>SYSTEM_STRING</code> converts to <code>STRING_8</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>SYSTEM_STRING</code> has a conversion query listing <code>STRING_8</code> as a conversion type, or
# Class <code>STRING</code> has a conversion procedure listing <code>SYSTEM_STRING</code> as a conversion type # Class <code>STRING_8</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. In this case <code>STRING_8</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> <code>
class STRING class STRING_8
… …
create create
make_from_cil make_from_cil
@@ -204,16 +204,16 @@ is equivalent to:
create my_string.make_from_cil (my_system_string) create my_string.make_from_cil (my_system_string)
</code> </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: So, we've seen how <code>SYSTEM_STRING</code> converts to <code>STRING_8</code>. But, in the context of our example, we could also do this:
<code> <code>
my_system_string := my_string my_system_string := my_string
</code> </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: Which means that <code>STRING_8</code> converts to <code>SYSTEM_STRING</code>. The <code>convert</code> part of class <code>STRING_8</code> also has a conversion query listing <code>SYSTEM_STRING</code> as a conversion type:
<code> <code>
class STRING class STRING_8
… …
create create
make_from_cil make_from_cil