<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=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class="">If you want to match [UInt8] specifically, just use the non-sugared definition:</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="color: #ba2da2" class="">extension</span> <span style="color: #4f8187" class="">RawBits</span> <span style="color: #ba2da2" class="">where</span> RawValue == Array<UInt8> {</div><div style="margin: 0px; line-height: normal; background-color: rgb(255, 255, 255); min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class="">}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class="">If you want it to match any array, that’s more complicated. As far as I’ve been able to work out, you have to wrap it in a protocol. Most of Array’s usefulness comes from protocols anyway, so you can probably use Sequence, Collection, or one or more of the more specific Mutable/RandomAccess/RangeReplaceableCollection protocols. </div><div style="margin: 0px; line-height: normal; background-color: rgb(255, 255, 255); min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><span style="color: #ba2da2" class="">extension</span> <span style="color: #4f8187" class="">RawBits</span> <span style="color: #ba2da2" class="">where</span> RawValue: Collection {</div><div style="margin: 0px; line-height: normal; background-color: rgb(255, 255, 255); min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class="">}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class="">If you really need an array specifically, as far as I can tell you have to use a pattern I’ve used for a similar purpose with optionals:</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; background-color: rgb(255, 255, 255);" class=""><div style="margin: 0px; font-size: 12px; line-height: normal; font-family: Helvetica; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: #ba2da2" class="">protocol</span> Arrayable {</div><div style="margin: 0px; line-height: normal; color: rgb(186, 45, 162);" class=""><span style="color: #000000" class=""> </span>associatedtype<span style="color: #000000" class=""> T</span></div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">func</span> asArray() -> [<span style="color: #703daa" class="">T</span>]</div><div style="margin: 0px; line-height: normal;" class="">}</div><div style="margin: 0px; font-size: 12px; line-height: normal; font-family: Helvetica; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; line-height: normal; color: rgb(186, 45, 162);" class="">extension<span style="color: #000000" class=""> </span><span style="color: #703daa" class="">Array</span><span style="color: #000000" class="">: </span><span style="color: #4f8187" class="">Arrayable</span><span style="color: #000000" class=""> {</span></div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">func</span> asArray() -> [<span style="color: #703daa" class="">Element</span>] {</div><div style="margin: 0px; line-height: normal; color: rgb(186, 45, 162);" class=""><span style="color: #000000" class=""> </span>return<span style="color: #000000" class=""> </span>self</div><div style="margin: 0px; line-height: normal;" class=""> }</div><div style="margin: 0px; line-height: normal;" class="">}</div><div style="margin: 0px; font-size: 12px; line-height: normal; font-family: Helvetica; min-height: 14px;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: #ba2da2" class="">extension</span> <span style="color: #4f8187" class="">RawBits</span> <span style="color: #ba2da2" class="">where</span> RawValue: Arrayable {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">func</span> foo() {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #ba2da2" class="">let</span> ary = <span style="color: #4f8187" class="">rawValue</span>.<span style="color: #31595d" class="">asArray</span>()</div><div style="margin: 0px; line-height: normal;" class=""> <span style="color: #008400" class="">// ary is now an Array.</span></div><div style="margin: 0px; line-height: normal;" class=""> }</div><div style="margin: 0px; line-height: normal;" class="">}</div><div class=""><br class=""></div><div class="">It’s rather unfortunate this requires a somewhat ugly workaround, but, well, it’s not the worst or most commonly encountered of the shortcomings in the type system.</div></div><div class=""><br class=""></div><div><blockquote type="cite" class=""><div class="">On Dec 13, 2017, at 9:42 PM, Frank Swarbrick via swift-users <<a href="mailto:swift-users@swift.org" class="">swift-users@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">I have the following:<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">public protocol RawBits: CustomStringConvertible, Collection {<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""> associatedtype RawValue<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""> var rawValue: RawValue { get set }<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">}<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">extension RawBits where RawValue: FixedWidthInteger, RawValue: UnsignedInteger {<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""> [...fields and methods are defined here...]<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">}<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">struct RawBits8: RawBits {<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""> var rawValue: UInt8<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">}<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">This all works fine.<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">Now I want to be able to define an extension to which the following would conform:<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">struct RawBitsX: RawBits {<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""> var rawValue: [UInt8]<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">}<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">rawValue is now an array rather than a simple type. I can't for the life of me figure out how to indicate this in the 'where' clause of an extension to RawBits. Can this be done? How?<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class=""><o:p class=""> </o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">Thanks for any assistance,<o:p class=""></o:p></span></div><div style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;" class=""><span style="font-size: 10pt; font-family: 'Courier New';" class="">Frank<o:p class=""></o:p></span></div></div><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">_______________________________________________</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; float: none; display: inline !important;" class="">swift-users mailing list</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><a href="mailto:swift-users@swift.org" style="color: rgb(149, 79, 114); text-decoration: underline; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">swift-users@swift.org</a><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><a href="https://lists.swift.org/mailman/listinfo/swift-users" style="color: rgb(149, 79, 114); text-decoration: underline; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" class="">https://lists.swift.org/mailman/listinfo/swift-users</a></div></blockquote></div><br class=""></body></html>