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Use of submethods in roles causes compiler to freeze #2250

vrurg opened this issue Sep 6, 2018 · 2 comments


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commented Sep 6, 2018

The Problem

When two roles define submethods with the same name if one consuming another and then been itself consumed by a class then compiler cannot deal with this and freezes without any message to the user.

Expected Behavior

Compilation must pass unless there is a rule restricting use of submethods in roles.

Steps to Reproduce

This code:

     role FooRole {
         submethod a {
             "this is FooRole::a";

     role BarRole does FooRole {
         submethod a {
             note "this is BarRole::a";

     class Foo does BarRole {
         submethod a {

effectively demonstrates the bug.


  • Operating system: macOS 10.13, Linux 4.15.0-33-generic #36-Ubuntu SMP
  • Compiler version (perl6 -v): This is Rakudo version 2018.06 built on MoarVM version 2018.06
    Tested with 2018.08 and 2017.10 too with same results.

@vrurg vrurg changed the title Use of submethods in roles might cause compiler to freeze Use of submethods in roles causes compiler to freeze Sep 6, 2018


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commented Feb 8, 2019

Part of the point of submethod is that it doesn't participate in the method resolution the same way as methods.

class A {
  submethod foo () { say 'A::foo' }

  method call-all-foo (){
    for self.^mro -> ::Type {
        if Type.can('foo') -> $_ {
class B is A {
class C is B {
  submethod foo () { say 'C::foo' }
# C::foo
# A::foo;
# No such method 'foo' for invocant of type 'B'. …

I think it makes sense for that to be extended so that a submethod in a role doesn't get composed in, but can still be called.

That is I think it should work this way:

role R {
  submethod foo () { say 'R::foo' }
class C does R {
# No such method 'foo' for invocant of type 'C'. …
# (currently this calls the `foo` in R)

# R::foo
# (currently this is an error)

I think that doing this will fix many issues around submethod being used in a role.

(Note that there needs to be tests that BUILD / TWEAK and DESTROY in a role get's called if this change happens.)


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commented Feb 8, 2019

@b2gills Thanks Brad! I think that your comment rather belongs to #2677.

This is my point of view too. submethod must solely belong to where it was declared. Period. To make iteration over submethods easier .^mro would require a named parameter to indicate willingness of the caller to accept both classes and roles.

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