Reference: isa

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')