<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><span class="Apple-tab-span" style="white-space:pre"> </span>I have already considered adding store properties to protocols before proposing abstract classes, but there are some issues : <div class=""><br class=""></div><div class="">1 - If protocols can have stored properties and default method implementation, how do you explain to newby the difference between a class and a protocol ? There is the same problem with Java 8 and interface which make learning to student really painfull….</div><div class="">In short words, protocol will became a sort of class and no longer a true kind of contract to conform to.</div><div class=""><br class=""></div><div class="">2 - What about compatibility with Objective C ?</div><div class=""><br class=""></div><div class="">3- more interesting problem : At the moment, multiple inheritance for protocol is allowed. When introducing store property in protocol, you introduce a major issue that C++ have : the diamond problem.</div><div class=""><br class=""></div><div class="">Example : </div><div class=""><br class=""></div><div class="">protocol A {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var value = 34</div><div class="">} <br class=""><div class=""><br class="webkit-block-placeholder"></div><div class="">protocol B {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>var value = 23</div><div class="">}</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">class</span> myClass : <span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">A</span>, <span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">B</span> {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span>func<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span>init<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> print("Value : \(value));</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">What should be print out ? how do you manage access to A.value and B.value ?</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><br class=""></div><div class="">
<div class=""><pre style="white-space: pre-wrap; background-color: rgb(255, 255, 255);" class=""></pre><blockquote type="cite" class=""><pre style="white-space: pre-wrap; background-color: rgb(255, 255, 255);" class="">Some people opposed to Abstract Classes proposal (including myself) have
said that mixins could solve the problem better.
So I prepaired a proposal draft to add stored properties to protocols. Here
it is:
<a href="https://gist.github.com/Anton3/f0550922c1be0fc5447c" class="">https://gist.github.com/Anton3/f0550922c1be0fc5447c</a>
P.S. I added a `mixin` keyword in the beginning, but we can opt to just
extend protocols, which I mention in "alternatives".</pre></blockquote><div class=""><br class=""></div></div>
</div>
<br class=""></div></body></html>