Documentation for method clone

Documentation for method clone, assembled from the following types:

class Mu

From Mu

(Mu) method clone

method clone(*%twiddles)

Creates a shallow clone of the invocant, including shallow cloning of private attributes. Alternative values for public attributes can be provided via named arguments with names matching the attributes' names.

class Point2D {
    has ($.x$.y);
    multi method gist(Point2D:D:{
        "Point($.x$.y)";
    }
}
 
my $p = Point2D.new(x => 2=> 3);
 
say $p;                     # OUTPUT: «Point(2, 3)␤» 
say $p.clone(=> -5);      # OUTPUT: «Point(2, -5)␤» 

Note that .clone does not go the extra mile to shallow-copy @. and %. sigiled attributes and, if modified, the modifications will still be available in the original object:

class Foo {
    has $.foo is rw = 42;
    has &.boo is rw = { say "Hi" };
    has @.bar       = <a b>;
    has %.baz       = <a b c d>;
}
 
my $o1 = Foo.new;
with my $o2 = $o1.clone {
    .foo = 70;
    .bar = <Z Y>;
    .baz = <Z Y X W>;
    .boo = { say "Bye" };
}
 
# Hash and Array attribute modifications in clone appear in original as well: 
say $o1;    # OUTPUT: «Foo.new(foo => 42, bar => ["Z", "Y"], baz => {:X("W"), :Z("Y")}, …␤» 
say $o2;    # OUTPUT: «Foo.new(foo => 70, bar => ["Z", "Y"], baz => {:X("W"), :Z("Y")}, …␤» 
$o1.boo.(); # OUTPUT: «Hi␤» 
$o2.boo.(); # OUTPUT: «Bye␤» 

To clone those, you could implement your own .clone that clones the appropriate attributes and passes the new values to Mu.clone, for example, via nextwith. Alternatively, your own .clone could clone self first (using self.Mu::clone or callsame) and then manipulate the clone as needed, before returning it.

class Bar {
    has @.foo = <a b>;
    has %.bar = <a b c d>;
    method clone { nextwith :foo(@!foo.clone:bar(%!bar.clone}
}
 
my $o1 = Bar.new;
with my $o2 = $o1.clone {
    .foo = <Z Y>;
    .bar = <Z Y X W>;
}
 
# Hash and Array attribute modifications in clone do not affect original: 
say $o1# OUTPUT: «Bar.new(foo => ["a", "b"], bar => {:a("b"), :c("d")})␤» 
say $o2# OUTPUT: «Bar.new(foo => ["Z", "Y"], bar => {:X("W"), :Z("Y")})␤» 

class Array

From Array

(Array) method clone

Defined as:

method clone(Array:D: --> Array:D)

Clones the original Array. Modifications of elements in the clone are not propagated to the original and vice-versa:

my @a = <a b c>my @b = @a.clone;
@b[1= 42@a.push: 72;
say @b# OUTPUT: «[a 42 c]␤» 
say @a# OUTPUT: «[a b c 72]␤» 

However, note that the reifier is shared between the two Arrays, so both Arrays will have the same elements even when each is randomly-generated on reification and each element will be reified just once, regardless of whether the reification was done by the clone or the original Array. Note: just as reifying an Array from multiple threads is not safe, so is, for example, reifying the clone from one thread while reifying the original from another thread is not safe.

my @a = 1{rand} … ∞; my @b = @a.clone;
say @b[^3]; # OUTPUT: «(1 0.0216426755282736 0.567660896142156)␤» 
say @a[^3]; # OUTPUT: «(1 0.0216426755282736 0.567660896142156)␤» 

class Date

From Date

(Date) method clone

Defined as:

method clone(:$year:$month:$day:&formatter)

Creates a new Date object based on the invocant, but with the given arguments overriding the values from the invocant.

say Date.new('2015-11-24').clone(month => 12);    # OUTPUT: «2015-12-24␤» 

class DateTime

From DateTime

(DateTime) method clone

Defined as:

method clone(:$year:$month:$day:$hour:$minute:$second:$timezone:&formatter)

Creates a new DateTime object based on the invocant, but with the given arguments overriding the values from the invocant.

say DateTime.new('2015-12-24T12:23:00Z').clone(hour => 0);
# OUTPUT: «2015-12-24T00:23:00Z␤» 

Note that this can lead to invalid dates in some circumstances:

say DateTime.new("2012-02-29T12:34:56Z").clone(year => 2015);
CATCH { default { put .^name''.Str } };
# OUTPUT: «X::OutOfRange: Day out of range. Is: 29, should be in 1..28␤»