Check-in [0299230758]

{"tip": {

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<th>#</th>
<th>Type</th>
<th>Tcl Version</th>
<th>Status</th>
<th>Title</th>
</tr></thead><tbody>








<tr class='project projectdraft projectdraft87 project87'>
<td valign='top'><a href='./tip/515.md'>515</a></td>
<td valign='top'>Project</td>
<td valign='top'>8.7</td>
<td valign='top'>Draft</td>
<td valign='top'># TIP 515: Level Value Reform</td>
</tr>

<th>#</th>
<th>Type</th>
<th>Tcl Version</th>
<th>Status</th>
<th>Title</th>
</tr></thead><tbody>

<tr class='project projectdraft projectdraft87 project87'>
<td valign='top'><a href='./tip/516.md'>516</a></td>
<td valign='top'>Project</td>
<td valign='top'>8.7</td>
<td valign='top'>Draft</td>
<td valign='top'># TIP 516: More OO Slot Operations</td>
</tr>
<tr class='project projectdraft projectdraft87 project87'>
<td valign='top'><a href='./tip/515.md'>515</a></td>
<td valign='top'>Project</td>
<td valign='top'>8.7</td>
<td valign='top'>Draft</td>
<td valign='top'># TIP 515: Level Value Reform</td>
</tr>

# TIP 516: More OO Slot Operations
	Author:         Donal K. Fellows <[email protected]>
	State:          Draft
	Type:           Project
	Vote:           Pending
	Created:        7-Sept-2018
	Post-History:   
	Tcl-Version:	8.7
	Keywords:       Tcl, TclOO
-----

# Abstract

This TIP proposes to add some more operations to slots by updating the class
that implements them.

# Rationale

Currently slots support **setting** (i.e., replacing all current slot items
with a different list of items), **appending** (i.e., adding onto the end of
the list), and **clearing** (i.e., setting the list to an empty list); the
former two cases are moderated by the need for slot items to be unique, but
that is a constraint enforced at the lower level. However, other basic
operations are conceivable too, such as **prepending** an item
and **removing** an item (with the latter needing a little care as it requires
normalisation of the slot items). An example of how this last use case might
be useful is when _removing_ a behaviour from an object by _removing_ a mixin
from it; that's possible to do with the existing code, but quite awkward
because it requires replacing the list of slot items with another list, and so
it is an operation that we should provide by default.

# Proposal

This will add two new methods to the `::oo::Slot` class:

  * _slot_ `-prepend` ?_item_ ...?

    This inserts the _item_ (or items) at the front of the list of items in
    the slot. If there are no such arguments given, this does nothing; it is
    not an error to prepend no items.

  * _slot_ `-remove` ?_item_ ...?

    This removes the _item_ (or items) from the list of items in the slot. If
    an _item_ is not present in the slot, this does nothing; it is not an
    error to remove a non-present item. If there are no such items in the
    arguments, this does nothing; it is not an error to remove no items.

# Implementation

To be done...

# Copyright

This document has been placed in the public domain.