[nem-bug] [Nemerle 0000841]: Nemerle compiler does not warn if there are polymorphic types with too deep inheritance tree

[feedback at nemerle.org]

A NOTE has been added to this issue.
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<http://nemerle.org/bugs/view.php?id=841> 
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Reported By:                nikov
Assigned To:                
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Project:                    Nemerle
Issue ID:                   841
Category:                   Compiler
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     new
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Date Submitted:             01-26-2007 20:19 CET
Last Modified:              01-26-2007 22:12 CET
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Summary:                    Nemerle compiler does not warn if there are
polymorphic types with too deep inheritance tree
Description: 
Nemerle compiler does not warn if there are polymorphic types with too deep
inheritance tree.

class A[T] { }
class B[T] : A[B[B[T]]] { }

_ = null : B[int]


This code produces System.TypeLoadException: A generic instantiation for
type
'A`1' from assembly 'NemerleProject, Version=1.0.0.0, Culture=neutral,
PublicKey
Token=null' was too deep.  Is this generic type defined or used
recursively?
   at _N_AutoModule.Main()

See Ecma-335, 9.2 Generics and recursive inheritance graphs
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----------------------------------------------------------------------
 nazgul - 01-26-07 21:41 
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I try with 

class A[T] { }
class B[T] : A[B[B[B[B[B[B[B[B[B[T]]]]]]]]]] { }

_ = null : B[B[B[int]]]

and it still works for me. Are you sure this is not a runtime issue
(recursive increase of generic type size)?

----------------------------------------------------------------------
 nazgul - 01-26-07 21:48 
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Ok, I can see in the spec that this should be disallowed at all...

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 nazgul - 01-26-07 22:00 
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Hehe, this is also not spotted by C# compiler:

class B<U> {}
class A<T> : B<A<A<T>>> {}

Reading the spec I can see that computing this verification graph is quite
costly operation (you should consider all generic types in program and
references libraries!). This is probably why C# compiler does not do
this... I guess we won't support it for the same reason and additionally
as we have no much resources in development and there are so much more
important tasks...

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 nikov - 01-26-07 22:12 
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Obviously, it is a bug in C# compiler.

Issue History
Date Modified  Username       Field                    Change              
======================================================================
01-26-07 20:19 nikov          New Issue                                    
01-26-07 21:41 nazgul         Note Added: 0001649                          
01-26-07 21:48 nazgul         Note Added: 0001650                          
01-26-07 22:00 nazgul         Note Added: 0001651                          
01-26-07 22:12 nikov          Note Added: 0001652                          
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