Add the `isa` operator

Adds a new infix operator named `isa`, with the semantics that

  $x isa SomeClass

is true if and only if `$x` is a blessed object reference that is either
`SomeClass` directly, or includes the class somewhere in its @ISA
hierarchy. It is false without warning or error for non-references or
non-blessed references.

This operator respects `->isa` method overloading, and is intended to
replace boilerplate code such as

  use Scalar::Util 'blessed';

  blessed($x) and $x->isa("SomeClass")

3 files changed, 35 insertions, 0 deletions

diff --git a/pod/perldelta.pod b/pod/perldelta.pod
index 23d3fe7656..664881286c 100644
--- a/pod/perldelta.pod
+++ b/pod/perldelta.pod
@@ -25,6 +25,15 @@ XXX New core language features go here.  Summarize user-visible core language
 enhancements.  Particularly prominent performance optimisations could go
 here, but most should go in the L</Performance Enhancements> section.
 
+=head2 The isa Operator
+
+A new experimental infix operator called C<isa> tests whether a given object
+is an instance of a given class or a class derived from it:
+
+    if( $obj isa Package::Name ) { ... }
+
+For more detail see L<perlop/Class Instance Operator>.
+
 [ List each enhancement as a =head2 entry ]
 
 =head1 Security
diff --git a/pod/perldiag.pod b/pod/perldiag.pod
index 465317bf92..593032610c 100644
--- a/pod/perldiag.pod
+++ b/pod/perldiag.pod
@@ -3262,6 +3262,12 @@ an anonymous subroutine, or a reference to a subroutine.
 (W overload) You tried to overload a constant type the overload package is
 unaware of.
 
+=item isa is experimental
+
+(S experimental::isa) This warning is emitted if you use the (C<isa>)
+operator. This operator is currently experimental and its behaviour may
+change in future releases of Perl.
+
 =item -i used with no filenames on the command line, reading from STDIN
 
 (S inplace) The C<-i> option was passed on the command line, indicating
diff --git a/pod/perlop.pod b/pod/perlop.pod
index c4eecd6c79..57bda73252 100644
--- a/pod/perlop.pod
+++ b/pod/perlop.pod
@@ -78,6 +78,7 @@ values only, not array values.
     nonassoc	named unary operators
     nonassoc	< > <= >= lt gt le ge
     nonassoc	== != <=> eq ne cmp ~~
+    nonassoc    isa
     left	&
     left	| ^
     left	&&
@@ -575,6 +576,25 @@ function, available in Perl v5.16 or later:
 
     if ( fc($x) eq fc($y) ) { ... }
 
+=head2 Class Instance Operator
+X<isa operator>
+
+Binary C<isa> evaluates to true when left argument is an object instance of
+the class (or a subclass derived from that class) given by the right argument.
+If the left argument is not defined, not a blessed object instance, or does
+not derive from the class given by the right argument, the operator evaluates
+as false. The right argument may give the class either as a barename or a
+scalar expression that yields a string class name:
+
+    if( $obj isa Some::Class ) { ... }
+
+    if( $obj isa "Different::Class" ) { ... }
+    if( $obj isa $name_of_class ) { ... }
+
+This is an experimental feature and is available from Perl 5.31.6 when enabled
+by C<use feature 'isa'>. It emits a warning in the C<experimental::isa>
+category.
+
 =head2 Smartmatch Operator
 
 First available in Perl 5.10.1 (the 5.10.0 version behaved differently),