isa

$io = $fd->isa(type)

• Returns true if the reference is blessed into package type or inherits from that package. Can be called as a static or object method call, or as a subroutine:
  
  

  UNIVERSAL::isa(val, type)
  

  
  
  Returns true if the first argument is a reference and either of the following is true:
  • val is a blessed reference and is blessed into package type or inherits from package type
  • val is a reference to a type of Perl variable (e.g., 'HASH')