<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="">Joe,<div class=""><br class=""></div><div class="">There seem to be many new syntactic features to support this, both inside and outside of a behavior. I was wondering if you had considered/had comments an alternative approach where you declare an ordinary new value type which meets certain rules and ‘wraps’ the existing type, then define new syntax/features in Swift for having the wrapper (or possibly even multiple levels of wrappers) be more transparent for use.</div><div class=""><br class=""></div><div class="">For instance, the existing ‘lazy’ keyword functionality might have been implemented by a type Lazy<T></div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">struct</span> Lazy<T> {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">private</span> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">var</span> val:<span style="font-variant-ligatures: no-common-ligatures; color: #6122ae" class="">T</span>?</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">let</span> supplier:()-><span style="font-variant-ligatures: no-common-ligatures; color: #6122ae" class="">T</span></div></div><div style="font-size: 11px;" class=""><p style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; min-height: 21px;" class=""> </p></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">init</span>(supplier:()-><span style="font-variant-ligatures: no-common-ligatures; color: #6122ae" class="">T</span>) {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">self</span>.<span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">supplier</span> = supplier</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; min-height: 21px;" class=""><br class=""></div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">var</span> value:<span style="font-variant-ligatures: no-common-ligatures; color: #6122ae" class="">T</span> {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">mutating</span> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">get</span> {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">if</span> <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">val</span> == <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">nil</span> {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">val</span> = <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">supplier</span>()</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">return</span> <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">val</span>!</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">set</span> {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">val</span> = <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">value</span></div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">mutating</span> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">func</span> clear() {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">val</span> = <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">nil</span></div><div style="margin: 0px; line-height: normal;" class=""> }</div><div class=""><br class=""></div></div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class="">}</div></div></blockquote><div class=""><br class=""></div><div class="">With the following as an example of use (without any additional syntactic features)</div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">var</span> globally = <span style="font-variant-ligatures: no-common-ligatures; color: #c91b13" class="">"Test"</span></div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">class</span> Foo {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">var</span> bar = <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">Lazy</span><<span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span>> {</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; color: rgb(201, 27, 19);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">globally</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> = </span>"Side effect"</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">return</span> <span style="font-variant-ligatures: no-common-ligatures; color: #0435ff" class="">1</span></div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class="">}</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; min-height: 21px;" class=""><br class=""></div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; color: rgb(83, 154, 164);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span>globally<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">)</span></div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; color: rgb(83, 154, 164);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3c828c" class="">Foo</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">().</span>bar<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span>value</div></div><div style="font-size: 11px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; color: rgb(83, 154, 164);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">(</span>globally<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">)</span></div><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; color: rgb(83, 154, 164);" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3c828c" class="">Foo</span>().bar.<span style="font-variant-ligatures: no-common-ligatures; color: #294c50" class="">clear</span>()</div></div></div></blockquote><div class=""><br class=""></div><div class="">One could opt into a syntax to allow value to be hidden from view. In fact, I can hide the use of the Lazy struct today if I’m willing to write more code:</div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">class</span> Foo {</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">private</span> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">var</span> internalbar = <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">Lazy</span><<span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span>> {</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; color: rgb(201, 27, 19);" class=""> <span style="color: rgb(195, 34, 117);" class="">return</span> <span style="color: rgb(4, 53, 255);" class="">1</span></div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">var</span> bar:<span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">Int</span> {</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">get</span> {</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo; color: rgb(83, 154, 164);" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">return</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""> </span>internalbar<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span>value</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #c32275" class="">set</span> {</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">internalbar</span>.<span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">value</span> = newValue</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""> }</div></div><div style="font-size: 8px;" class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class="">}</div></div><div class=""><div style="margin: 0px; font-size: 14px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #3d1d81" class="">print</span>(<span style="font-variant-ligatures: no-common-ligatures; color: #3c828c" class="">Foo</span>().<span style="font-variant-ligatures: no-common-ligatures; color: #539aa4" class="">bar</span>)</div></div></blockquote><div class=""><br class=""></div><div class="">Which actually has the benefit of being able to call the clear() method without new syntax, and being able to control access to clear separate from the getter/setter</div><div class=""><br class=""></div><div class="">-DW</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><div><blockquote type="cite" class=""><div class="">On Jan 13, 2016, at 3:07 PM, Joe Groff via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Thanks everyone for the first round of feedback on my behaviors proposal. I've revised it with the following changes:<br class=""><br class="">- Instead of relying on mapping behaviors to function or type member lookup, I've introduced a new purpose-built 'var behavior' declaration, which declares the accessor and initializer requirements and provides the storage and behavior methods of the property. I think this gives a clearer design for authoring behaviors, and allows for a more efficient and flexible implementation model.<br class="">- I've backed off from trying to include 'let' behaviors. As many of you noted, it's better to tackle immutable computed properties more holistically than to try to backdoor them in.<br class="">- I suggest changing the declaration syntax to use a behavior to square brackets—'var [behavior] foo'—which avoids ambiguity with destructuring 'var' bindings, and also works with future candidates for behavior decoration, particularly `subscript`.<br class=""><br class="">Here's the revised proposal:<br class=""><br class=""><a href="https://gist.github.com/jckarter/50b838e7f036fe85eaa3" class="">https://gist.github.com/jckarter/50b838e7f036fe85eaa3</a><br class=""><br class="">For reference, here's the previous iteration:<br class=""><br class="">https://gist.github.com/jckarter/f3d392cf183c6b2b2ac3<br class=""><br class="">Thanks for taking a look!<br class=""><br class="">-Joe<br class="">_______________________________________________<br class="">swift-evolution mailing list<br class="">swift-evolution@swift.org<br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></div></blockquote></div><br class=""></div></body></html>