# TIP 473: Allow a Defined Target Namespace in oo::copy
	State:		Final
	Type:		Project
	Tcl-Version:	8.6.7
	Vote:		Done
	Post-History:	
	Author:		Donal Fellows <dkf@users.sf.net>
	Created:	06-Jun-2017
	Keywords:	Tcl, missing functionality, bugfix
	Tcl-Branch:	oo-copy-ns
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# Abstract

This TIP adds functionality to **oo::copy** to allow the created copy to
have a defined namespace, much as **oo::class**'s **createWithNamespace**
method allows such a namespace to be given on normal object creation.

# Rationale

Due to an oversight, the **oo::copy** command is missing the ability to have
an explicit namespace name specified to use as the instance namespace of the
target object. It was always intended to have this \(and the functionality is
there in the C API\), but it was omitted from the Tcl-level interface.

Having this capability allows objects to be used as factories for namespaces,
which is in many ways an inversion of the way that TclOO was designed \(with
namespaces as the basis for objects\). It was requested by Nathan Coulter as a
way to enable more complex behaviour in Rivet and NaviServer. See Tcl Issue
dd3b844fda <https://core.tcl-lang.org/tcl/tktview/dd3b844fdabdeae5fcb0>  for more
information.

# Proposed Change

I propose to add one more optional argument to **oo::copy**,
_targetNamespace_, that if provided and non-empty will be the name of a
namespace \(resolved relative to the current namespace if not an absolute name\)
that will be the name of the newly created target object's instance namespace.
The named namespace must not already exist. Note that specifying the
_targetObject_ as the empty string will cause the object's command to be
automatically chosen.

 > **oo::copy** _sourceObject_ ?_targetObject_? ?_targetNamespace_?

The meaning of the result of the command is unchanged.

# Implementation

See the oo-copy-ns branch. <https://core.tcl-lang.org/tcl/timeline?r=oo-copy-ns> 

# Copyright

This document has been placed in the public domain.

