Clean up various is rw misuses.

It's meaningless on non-Scalars. In some places, drop bogus `is rw`,
and in others switch to using scalars over \foo.

src/core/Any.pm

@@ -388,20 +388,19 @@ proto sub infix:<after>(Mu $, Mu $?) is pure { * }
 multi sub infix:<after>($x?)       { Bool::True }
 multi sub infix:<after>(\a, \b)    { (a cmp b) > 0 }
 
-# XXX: should really be '$a is rw' (no \) in the next four operators
 proto prefix:<++>(|)             { * }
-multi prefix:<++>(Mu:D \a is rw) { a = a.succ }
-multi prefix:<++>(Mu:U \a is rw) { a = 1 }
+multi prefix:<++>(Mu:D $a is rw) { $a = $a.succ }
+multi prefix:<++>(Mu:U $a is rw) { $a = 1 }
 proto prefix:<-->(|)             { * }
-multi prefix:<-->(Mu:D \a is rw) { a = a.pred }
-multi prefix:<-->(Mu:U \a is rw) { a = -1 }
+multi prefix:<-->(Mu:D $a is rw) { $a = $a.pred }
+multi prefix:<-->(Mu:U $a is rw) { $a = -1 }
 
 proto postfix:<++>(|)             { * }
-multi postfix:<++>(Mu:D \a is rw) { my $b = a; a = a.succ; $b }
-multi postfix:<++>(Mu:U \a is rw) { a = 1; 0 }
+multi postfix:<++>(Mu:D $a is rw) { my $b = $a; $a = $a.succ; $b }
+multi postfix:<++>(Mu:U $a is rw) { $a = 1; 0 }
 proto postfix:<-->(|)             { * }
-multi postfix:<-->(Mu:D \a is rw) { my $b = a; a = a.pred; $b }
-multi postfix:<-->(Mu:U \a is rw) { a = -1; 0 }
+multi postfix:<-->(Mu:D $a is rw) { my $b = $a; $a = $a.pred; $b }
+multi postfix:<-->(Mu:U $a is rw) { $a = -1; 0 }
 
 proto sub pick(|) { * }
 multi sub pick($n, +values) { values.pick($n) }

src/core/Baggy.pm

@@ -158,7 +158,7 @@ my role Baggy does QuantHash {
     }
 
     sub ROLLPICKGRABN(                                        # N times
-      $self, $count, @pairs is rw, :$keep
+      $self, $count, @pairs, :$keep
     ) {
         my Int $total = $self.total;
         my Int $rand;

src/core/Bool.pm

@@ -33,10 +33,10 @@ my class Bool { # declared in BOOTSTRAP
     }
 }
 
-multi sub prefix:<++>(Bool:U \a is rw)  { a = True; }
-multi sub prefix:<-->(Bool:U \a is rw)  { a = False; }
-multi sub postfix:<++>(Bool:U \a is rw) { a = True; False; }
-multi sub postfix:<-->(Bool:U \a is rw) { a = False; }
+multi sub prefix:<++>(Bool:U $a is rw)  { $a = True; }
+multi sub prefix:<-->(Bool:U $a is rw)  { $a = False; }
+multi sub postfix:<++>(Bool:U $a is rw) { $a = True; False; }
+multi sub postfix:<-->(Bool:U $a is rw) { $a = False; }
 
 proto sub prefix:<?>(Mu $) is pure { * }
 multi sub prefix:<?>(Bool:D \a) { a }

src/core/CompUnit.pm

@@ -99,7 +99,7 @@ RAKUDO_MODULE_DEBUG("Precomping with %*ENV<RAKUDO_PRECOMP_WITH>")
 
     proto method load(CompUnit:D: |) { * }
     multi method load(CompUnit:D: ) { self.load(Any) }
-    multi method load(CompUnit:D: \GLOBALish is rw, :$line) {
+    multi method load(CompUnit:D: \GLOBALish, :$line) {
         $global.protect( {
             RAKUDO_MODULE_DEBUG("going to load $!name") if $?RAKUDO_MODULE_DEBUG;
 

src/core/CompUnitRepo/Local/Installation.pm

@@ -50,7 +50,7 @@ sub MAIN(:$name, :$auth, :$ver, *@, *%) {
                 SORRY
             my %caps = :name([\'Distribution\', 12]), :auth([\'Author(ity)\', 11]), :ver([\'Version\', 7]);
             for @binaries -> $dist {
-                for %caps.kv -> $caption, @opts is rw {
+                for %caps.kv -> $caption, @opts {
                     @opts[1] = max @opts[1], ($dist{$caption} // \'\').Str.chars
                 }
             }