Language hole or wrong implementation?
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Question,
Is the following valid Eiffel code? It compiles and executes (with
unexpected results) in Visual Eiffel 2.0.
Synopsis: -----------
"Eiffel: The Language" says that given a generic class G, G[A]
conforms to G[B], as long as A is an ancestor of B. Assuming the above
is true, how does the language safeguard against the following:
0) Assume:
- B derives from A
- generic class G[T] has method 'setAttr(val:T)',
- class U has methods 'make' and 'test(g : G[A])'
1) Method 'make' of class U creates an instance, named g, of G[B],
2) and then it calls 'test ( g )',
3) Method 'test( g: G[A] )' creates an instance of A, named a, and
then calls 'g.setAttr(a)'
In the above scenario, we have called 'setAttr ( val : B )' with a
non-conforming argument (i.e. of type A).
-----------------
The source files that compile and run in Visual Eiffel are attached.
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Question,
<P>Is the following valid Eiffel code? It compiles and executes (with
unexpected results) in Visual Eiffel 2.0.
<P>Synopsis: -----------
<BR> "Eiffel: The Language" says that given a generic class G, G[A]
conforms to G[B], as long as A is an ancestor of B. Assuming the
above is true, how does the language safeguard against the following:
<BR> 0) Assume:
<BR> - B derives from A
<BR> - generic class G[T] has
method 'setAttr(val:T)',
<BR> - class U has methods 'make'
and 'test(g : G[A])'
<BR> 1) Method 'make' of class U creates an instance, named g, of
G[B],
<BR> 2) and then it calls 'test ( g )',
<BR> 3) Method 'test( g: G[A] )' creates an instance of A, named
a, and then calls 'g.setAttr(a)'
<P> In the above scenario, we have called 'setAttr ( val :
B )' with a non-conforming argument (i.e. of type A).
<BR>-----------------
<P>The source files that compile and run in Visual Eiffel are attached.</HTML>
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