X10

Constraints on type parameters in method formals aren't added to the environment used to typecheck the method body

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  • Testcase included:
    yes
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Description

Compiling

import x10.util.Ordered;
public class LessIsMore{
   static def doIt[T](a: T{T <: Ordered[T]}) {
      return a < a;
   }
}

yields

LessIsMore.x10:4: No valid method call found for call in given type.    
     	 Call: operator<(T, T)    
     	 Type: x10.lang.Any

Can you explain what this error message means? I thought that T<:Ordered[T] meant "T implements Ordered[T]"
and therefore (since "<" is in that interface) I ought to be able to use it.

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Igor Peshansky added a comment -

This is a bug in propagating type constraints from method arguments into the environment. A workaround for now is to move the type constraint into the method guard, namely:

import x10.util.Ordered;
public class LessIsMore {
  static def doIt[T](a: T){T <: Ordered[T]} {
    return a < a;
  }
}
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Igor Peshansky added a comment - This is a bug in propagating type constraints from method arguments into the environment. A workaround for now is to move the type constraint into the method guard, namely: import x10.util.Ordered; public class LessIsMore { static def doIt[T](a: T){T <: Ordered[T]} { return a < a; } }
Igor Peshansky made changes -
Field Original Value New Value
Fix Version/s X10 2.2 [ 16002 ]
Affects Version/s X10 2.1.2 [ 16498 ]
Component/s X10 Compiler: Front-end Constraints [ 14507 ]
Component/s X10 Compiler: Front-end [ 13471 ]
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Jonathan Brezin added a comment -

Thanks. It does work in my "real" code. It occurred to me that there is a situation where you really might want to attach the constraint to the argument. 

def doIt[T]{a:T{T <: Ordered[T]}, b: T) { /* need "a" ordered, but not b */ }

Not all subtypes of T need implement Ordered[T], but it may be important that the first argument should. So it does make sense to put some effort into fixing the constraint propagation.

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Jonathan Brezin added a comment - Thanks. It does work in my "real" code. It occurred to me that there is a situation where you really might want to attach the constraint to the argument. def doIt[T]{a:T{T <: Ordered[T]}, b: T) { /* need "a" ordered, but not b */ } Not all subtypes of T need implement Ordered [T] , but it may be important that the first argument should. So it does make sense to put some effort into fixing the constraint propagation.
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Igor Peshansky added a comment -

Sorry, it doesn't work that way. You are not constraining a and b, you are constraining T. And the constraint is in effect for the whole method. So either both a and b are ordered, or neither is (because they are the same type, T). Since T is defined by doIt(), you may as well put the constraint into the method guard.

If you want two potentially different types, you have to use two different type variables.

The meaning you tried to assign to this idiom above is actually captured by XTENLANG-683.

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Igor Peshansky added a comment - Sorry, it doesn't work that way. You are not constraining a and b , you are constraining T . And the constraint is in effect for the whole method. So either both a and b are ordered, or neither is (because they are the same type, T ). Since T is defined by doIt() , you may as well put the constraint into the method guard. If you want two potentially different types, you have to use two different type variables. The meaning you tried to assign to this idiom above is actually captured by XTENLANG-683 .
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Jonathan Brezin added a comment -

Again thanks: I'll make sure I explain this clearly in the Guide.

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Jonathan Brezin added a comment - Again thanks: I'll make sure I explain this clearly in the Guide.
Igor Peshansky made changes -
Link This issue is depended upon by XTENLANG-2584 [ XTENLANG-2584 ]
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Igor Peshansky added a comment -

Defer to 2.2.1.

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Igor Peshansky added a comment - Defer to 2.2.1.
Igor Peshansky made changes -
Fix Version/s X10 2.2.1 [ 17131 ]
Fix Version/s X10 2.2 [ 16002 ]
Igor Peshansky made changes -
Link This issue is depended upon by XTENLANG-2584 [ XTENLANG-2584 ]
David Grove made changes -
Summary What does Ordered interface mean? Another strange error message Constraints on type parameters in method guards aren't added to the environment used to typecheck the method body
David Grove made changes -
Summary Constraints on type parameters in method guards aren't added to the environment used to typecheck the method body Constraints on type parameters in method formals aren't added to the environment used to typecheck the method body
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David Grove added a comment -

bulk defer of open issues to 2.2.2.

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David Grove added a comment - bulk defer of open issues to 2.2.2.
David Grove made changes -
Fix Version/s X10 2.2.2 [ 17639 ]
Fix Version/s X10 2.2.1 [ 17131 ]
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David Grove added a comment -

bulk defer of issues to 2.2.3.

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David Grove added a comment - bulk defer of issues to 2.2.3.
David Grove made changes -
Fix Version/s X10 2.2.3 [ 18146 ]
Fix Version/s X10 2.2.2 [ 17639 ]
David Grove made changes -
Assignee Igor Peshansky [ ipeshansky ]
David Grove made changes -
Fix Version/s X10 2.3 [ 17009 ]
Fix Version/s X10 2.2.3 [ 18146 ]
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David Grove added a comment -

bulk defer of 2.3.0 open issues to 2.3.1.

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David Grove added a comment - bulk defer of 2.3.0 open issues to 2.3.1.
David Grove made changes -
Fix Version/s X10 2.3.1 [ 18657 ]
Fix Version/s X10 2.3 [ 17009 ]
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David Grove added a comment -

bulk defer to 2.3.2

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David Grove added a comment - bulk defer to 2.3.2
David Grove made changes -
Fix Version/s X10 2.3.2 [ 19010 ]
Fix Version/s X10 2.3.1 [ 18657 ]

People

  • Assignee:
    Unassigned
    Reporter:
    Jonathan Brezin
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    Updated: