=begin pod

=TITLE class X::Signature::Placeholder

=SUBTITLE Compilation error due to placeholders in a block with a signature

=for code :skip-test
class X::Signature::Placeholder does X::Comp { }

Compile time error thrown when a block has both an explicit signature
and placeholder parameters.

For example

=for code :skip-test
sub f() { $^x }

dies with

=for code :skip-test
===SORRY!===
Placeholder variable '$^x' cannot override existing signature

=head1 Methods

=head2 method placeholder

    method placeholder() returns Str:D

Returns the name of a placeholder that was used in a block that already
had a signature.

=end pod
