From @smls

The behavior is different for the various syntax forms for looking up symbols dynamically​:

A) The [sigil at the start; null pseudo-package; name in curly or angle brackets] form throws an "Index out of bounds" error​:

  $ perl6-m -e 'say defined $​::{"foo"}'
  ===SORRY!===
  MVMArray​: Index out of bounds
 
  $ perl6-m -e 'say defined $​::<foo>'
  ===SORRY!===
  MVMArray​: Index out of bounds
 
  $ perl6-m -e 'say defined &​::<foo>'
  ===SORRY!===
  MVMArray​: Index out of bounds

B) The [sigil at the start; *named* pseudo-package; name in curly or angle brackets] form fails with "Undeclared routine​: &MY" or similar if the sigil is &, but works fine for other sigils​:

  say defined &MY​::{"foo"}'
  ===SORRY!=== Error while compiling -e
  Undeclared routine​:
  &MY used at line 1
 
  $ perl6-m -e 'say defined &MY​::<foo>'
  ===SORRY!=== Error while compiling -e
  Undeclared routine​:
  &MY used at line 1
 
  $ perl6-m -e 'say defined $MY​::<foo>'
  False

C) The remaining forms seem to work fine.

In particular all the ones that use parens instead of curly/angle brackets to look up the name​:

  $ perl6 -e 'say .defined for &​::("foo"), &MY​::("foo"), $MY​::("foo")
  False
  False
  False

As well as the ones that treat the sigil as part of the name​:

  $ perl6 -e 'say .defined for :​:<$foo>, :​:<&foo>, MY​::<&foo>'
  False
  False
  False

From @AlexDaniel

As of today (2017.11,HEAD(e5b660e)) it gives this​:

===SORRY!=== Error while compiling -e
Variable '$' is not declared
at -e​:1
------> say defined ⏏$​::<foo>

There was another ticket that had exactly the same change of an error message, perhaps worth searching for it (ping me if you really want to find it).

On 2015-02-22 14​:03​:46, smls75@​gmail.com wrote​:

The behavior is different for the various syntax forms for looking up
symbols dynamically​:

A) The [sigil at the start; null pseudo-package; name in curly or
angle brackets] form throws an "Index out of bounds" error​:

$ perl6-m -e 'say defined $​::{"foo"}'
===SORRY!===
MVMArray​: Index out of bounds

$ perl6-m -e 'say defined $​::<foo>'
===SORRY!===
MVMArray​: Index out of bounds

$ perl6-m -e 'say defined &​::<foo>'
===SORRY!===
MVMArray​: Index out of bounds

B) The [sigil at the start; *named* pseudo-package; name in curly or
angle brackets] form fails with "Undeclared routine​: &MY" or similar
if the sigil is &, but works fine for other sigils​:

say defined &MY​::{"foo"}'
===SORRY!=== Error while compiling -e
Undeclared routine​:
&MY used at line 1

$ perl6-m -e 'say defined &MY​::<foo>'
===SORRY!=== Error while compiling -e
Undeclared routine​:
&MY used at line 1

$ perl6-m -e 'say defined $MY​::<foo>'
False

C) The remaining forms seem to work fine.

In particular all the ones that use parens instead of curly/angle
brackets to look up the name​:

$ perl6 -e 'say .defined for &​::("foo"), &MY​::("foo"), $MY​::("foo")
False
False
False

As well as the ones that treat the sigil as part of the name​:

$ perl6 -e 'say .defined for :​:<$foo>, :​:<&foo>, MY​::<&foo>'
False
False
False

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