clone#

Make an independent copy of the current digest state.

Synopsis#

my $copy = $ctx->clone;

What you get back#

A new Digest::MD5 object whose internal state is a byte-for-byte copy of the original — same accumulated length, same four state words, same partial-block buffer. The two contexts are independent afterwards: further add calls on one do not affect the other. The class of the returned object matches the class of $ctx, so cloning a subclass instance yields a subclass instance.

The primary use is peeking at an intermediate digest without destroying the ongoing computation. Because digest / hexdigest / b64digest reset the context, the pattern $ctx->clone->hexdigest is how you extract a snapshot and keep hashing.

Examples#

Per-line running digest over a stream:

my $ctx = Digest::MD5->new;
while (my $line = <$fh>) {
    $ctx->add($line);
    print "after line $.: ", $ctx->clone->hexdigest, "\n";
}
my $final = $ctx->hexdigest;    # digest of the whole stream

Fork a digest to feed two suffixes:

my $base = Digest::MD5->new;
$base->add("common prefix ");

my $a = $base->clone->add("suffix A")->hexdigest;
my $b = $base->clone->add("suffix B")->hexdigest;

Edge cases#

Cloning immediately after new yields a context equivalent to a fresh Digest::MD5->new.
Cloning an object whose state was restored via context copies that restored state, not a fresh one.

Differences from upstream#

Fully compatible with upstream Digest::MD5 2.58.