From @masak

<masak> m​: class C { has $.x = 42; submethod BUILD(​:$.x) {} }; say C.new.x
<camelia> rakudo-moar fadca9​: OUTPUT«Cannot find method 'STORE'␤ in
submethod BUILD [...]
<masak> m​: class C { has $.x = 42; submethod BUILD(​:$!x = 5) { $.x }
}; say C.new.x
<camelia> rakudo-moar fadca9​: OUTPUT«===SORRY!=== Error [...] Virtual
call $.x may not be used on partially constructed objects [...]
<masak> that "Virtual call" error message should probably happen for
:$.x as well...
* masak submits rakudobug

Even if using :$.x in a parameter list in a submethod is OK, the error
message "Cannot find method 'STORE'" is rather less-than-awesome and
mysterious as it stands.

From @jnthn

On Fri Jul 10 07​:02​:13 2015, masak wrote​:

<masak> m​: class C { has $.x = 42; submethod BUILD(​:$.x) {} }; say C.new.x
<camelia> rakudo-moar fadca9​: OUTPUT«Cannot find method 'STORE'␤ in
submethod BUILD [...]
<masak> m​: class C { has $.x = 42; submethod BUILD(​:$!x = 5) { $.x }
}; say C.new.x
<camelia> rakudo-moar fadca9​: OUTPUT«===SORRY!=== Error [...] Virtual
call $.x may not be used on partially constructed objects [...]
<masak> that "Virtual call" error message should probably happen for
:$.x as well...
* masak submits rakudobug

Even if using :$.x in a parameter list in a submethod is OK, the error
message "Cannot find method 'STORE'" is rather less-than-awesome and
mysterious as it stands.

Well, nothing too mysterious in so far as we're not initialized enough yet to have storage set up. But yeah, it should never make it that far. Now​:

===SORRY!=== Error while compiling -e
Virtual call $.x may not be used on partially constructed objects
at -e​:1
------> s C { has $.x = 42; submethod BUILD(​:$.x<HERE>) {} }

Test added to S12-methods/attribute-params.t.

The RT System itself - Status changed from 'new' to 'open'

@jnthn - Status changed from 'open' to 'resolved'