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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Thanks Youming,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">That’s not quite what I meant. I may have misinterpreted what Tony was saying though.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">I wanted to do conversion on String, not the containing type. The problem of doing it on the containing type is that as soon as you need one field to be custom, you’re roped into handling
all the others. For a small struct, not a big deal, for larger ones, it is. Something like this is what I tried:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">import Cocoa<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">let jsonString = "{" +<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> "\"name\": \"Endeavor\"," +<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> "\"abv\": 8.9," +<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> "\"brewery\": \"Saint Arnold\"," +<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> "\"style\": \"ipa\"}"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">struct Beer: Codable {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> let name: String<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> let abv: String<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> let brewery: String<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> let style: String<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">}<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">extension String {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> init(from decoder: Decoder) throws {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> print("i got hit.")<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> let value = try decoder.singleValueContainer().decode(String.self)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> self.init(value)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"> }<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">}<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">let jsonData = jsonString.data(using: .utf8)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">let decoder = JSONDecoder()<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">let beer = try! decoder.decode(Beer.self, from: jsonData!)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:Calibri">fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.typeMismatch(Swift.String, Swift.DecodingError.Context(codingPath: [__lldb_expr_17.Beer.(CodingKeys in
_C8902E33F84CE6946081129DAF1824E1).abv], debugDescription: "Expected to decode String but found a number instead.", underlyingError: nil)): file /Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-900.0.59/src/swift/stdlib/public/core/ErrorType.swift,
line 181</span></b><span style="font-size:11.0pt;font-family:Calibri"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span style="font-family:Calibri;color:black">From: </span>
</b><span style="font-family:Calibri;color:black">Youming Lin <ylin@us.ibm.com><br>
<b>Date: </b>Wednesday, August 30, 2017 at 2:35 PM<br>
<b>To: </b>"Sneed, Brandon" <brsneed@ebay.com><br>
<b>Cc: </b>Tony Parker <anthony.parker@apple.com>, "swift-corelibs-dev@swift.org" <swift-corelibs-dev@swift.org>, "swift-corelibs-dev-bounces@swift.org" <swift-corelibs-dev-bounces@swift.org><br>
<b>Subject: </b>Re: [swift-corelibs-dev] Adding type conversion capabilities to JSON encode/decode<o:p></o:p></span></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<p><span style="font-size:10.0pt">Brandon<br>
<br>
I cooked up a simple example and it works as expected.<br>
<br>
</span><span style="font-family:Monaco">ylin@youming-mbpr:~/Swift/Configuration$ swift</span><br>
<span style="font-family:Monaco">Welcome to Apple Swift version 4.0-dev (LLVM 2dedb62a0b, Clang b9d76a314c, Swift 0899bd328a). Type :help for assistance.</span><br>
<span style="font-family:Monaco">1> import Foundation</span><br>
<span style="font-family:Monaco">2> struct A: Codable { </span><br>
<span style="font-family:Monaco">3. var integer: Int </span><br>
<span style="font-family:Monaco">4. </span><br>
<span style="font-family:Monaco">5. public init(integer: Int) { </span><br>
<span style="font-family:Monaco">6. self.integer = integer </span><br>
<span style="font-family:Monaco">7. } </span><br>
<span style="font-family:Monaco">8. </span><br>
<span style="font-family:Monaco">9. public init(from decoder: Decoder) throws { </span>
<br>
<span style="font-family:Monaco">10. print("Custom decoder") </span><br>
<span style="font-family:Monaco">11. let container = try decoder.container(keyedBy: CodingKeys.self)
</span><br>
<span style="font-family:Monaco">12. integer = try container.decode(Int.self, forKey: .integer)
</span><br>
<span style="font-family:Monaco">13. } </span><br>
<span style="font-family:Monaco">14. } </span><br>
<span style="font-family:Monaco">15. </span><br>
<span style="font-family:Monaco">16. try! JSONDecoder().decode(A.self, from: JSONEncoder().encode(A(integer: 42)))</span><br>
<span style="font-family:Monaco">Custom decoder</span><br>
<span style="font-family:Monaco">$R0: A = {</span><br>
<span style="font-family:Monaco">integer = 42</span><br>
<span style="font-family:Monaco">}</span><span style="font-size:10.0pt"><br>
</span><br>
<span style="font-size:10.0pt">You should be able to implement your custom init to convert the number into a string and JSONDecoder should use that automatically.<br>
</span><br>
<span style="font-size:10.0pt">Thanks,<br>
<br>
Youming Lin<br>
IBM Cloud, Swift@IBM, Kitura developer<br>
Austin, TX<br>
GitHub: @youming-lin</span><br>
<br>
<img width="16" height="16" id="_x0000_i1025" src="cid:image001.gif@01D3219E.3340CAF0" alt="nactive hide details for "Sneed, Brandon" ---08/30/2017 04:14:57 PM---Tha"><span style="font-size:10.0pt;color:#424282">"Sneed, Brandon" ---08/30/2017 04:14:57 PM---Thanks
Youming, Ok, thanks! I did try that, but I can’t seem to figure out how to make it actually</span><br>
<br>
<span style="font-size:10.0pt;color:#5F5F5F">From: </span><span style="font-size:10.0pt">"Sneed, Brandon" <brsneed@ebay.com></span><br>
<span style="font-size:10.0pt;color:#5F5F5F">To: </span><span style="font-size:10.0pt">Youming Lin <ylin@us.ibm.com></span><br>
<span style="font-size:10.0pt;color:#5F5F5F">Cc: </span><span style="font-size:10.0pt">Tony Parker <anthony.parker@apple.com>, "swift-corelibs-dev@swift.org" <swift-corelibs-dev@swift.org>, "swift-corelibs-dev-bounces@swift.org" <swift-corelibs-dev-bounces@swift.org></span><br>
<span style="font-size:10.0pt;color:#5F5F5F">Date: </span><span style="font-size:10.0pt">08/30/2017 04:14 PM</span><br>
<span style="font-size:10.0pt;color:#5F5F5F">Subject: </span><span style="font-size:10.0pt">Re: [swift-corelibs-dev] Adding type conversion capabilities to JSON encode/decode</span><o:p></o:p></p>
<div class="MsoNormal">
<hr size="2" width="100%" noshade="" style="color:#8091A5" align="left">
</div>
<p class="MsoNormal"><br>
<br>
<br>
Thanks Youming,<br>
<br>
Ok, thanks! I did try that, but I can’t seem to figure out how to make it actually get used in the decoding process. That being my preferred way, I tried it first. I chalked it not working up to Swift not knowing which of the 2 init(from decoder:) functions
to call, mine or theirs. But, maybe there’s something I’m missing here.<br>
<br>
Any insight is appreciated.<br>
<br>
Thanks!<br>
<br>
<br>
<br>
Brandon Sneed<br>
<br>
<b>From: </b>Youming Lin <ylin@us.ibm.com><b><br>
Date: </b>Wednesday, August 30, 2017 at 1:18 PM<b><br>
To: </b>"Sneed, Brandon" <brsneed@ebay.com><b><br>
Cc: </b>Tony Parker <anthony.parker@apple.com>, "swift-corelibs-dev@swift.org" <swift-corelibs-dev@swift.org>, "swift-corelibs-dev-bounces@swift.org" <swift-corelibs-dev-bounces@swift.org><b><br>
Subject: </b>Re: [swift-corelibs-dev] Adding type conversion capabilities to JSON encode/decode<o:p></o:p></p>
<p><span style="font-size:10.0pt">Brandon<br>
<br>
></span>JSON’s types effectively end up matching specifically to primitives, of which there is no mechanism to override the behavior of how a String gets decoded for instance.<span style="font-size:10.0pt"><br>
<br>
You can override the default behavior with your own custom init(from:) implementation for your Codable struct:
</span><a href="https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Furldefense.proofpoint.com%2Fv2%2Furl%3Fu%3Dhttps-3A__na01.safelinks.protection.outlook.com_-3Furl-3Dhttps-253A-252F-252Fdeveloper.apple.com-252Fdocumentation-252Fswift-252Fdecodable-252F2894081-2Dinit-26data-3D02-257C01-257Cbrsneed-2540ebay.com-257C6290a819253b47b0eb2408d4efe454ae-257C46326bff992841a0baca17c16c94ea99-257C0-257C0-257C636397211330551372-26sdata-3DoLr1Q10-252BztzwG-252BCXpMinBzJNTwSy-252FjoBsKm9Glg1-252FxY-253D-26reserved-3D0%26d%3DDwMGaQ%26c%3Djf_iaSHvJObTbx-siA1ZOg%26r%3DgkRZBtsmKeGPCOlAIRJoOA%26m%3Dc3lYikOfd2-4q_nd_qMnJ4gXKIuKuxxoJRxIrIZc3Hw%26s%3Dh1azblXptqRwHqDQhejN9sSFa8dR-Gd8OkB7_6VwgNg%26e%3D&data=02%7C01%7Cbrsneed%40ebay.com%7Cebd9669255614ce4dccc08d4efef218c%7C46326bff992841a0baca17c16c94ea99%7C0%7C0%7C636397257717072726&sdata=TIZrCfocLCJGcfOj%2B9V2FEiXPSTKN4hnL1Rm03GqHvk%3D&reserved=0"><span style="font-size:10.0pt">https://developer.apple.com/documentation/swift/decodable/2894081-init</span></a><span style="font-size:10.0pt"><br>
<br>
You can check Foundation source code (i.e., the URL struct) on how this can be implemented.</span><br>
<span style="font-size:10.0pt"><br>
Thanks,<br>
<br>
Youming Lin<br>
IBM Cloud, Swift@IBM, Kitura developer<br>
Austin, TX<br>
GitHub: @youming-lin</span><br>
<br>
<img border="0" width="16" height="16" id="_x0000_i1027" src="cid:image002.gif@01D3219E.3340CAF0" alt="active hide details for "Sneed, Brandon via swift-corelibs-dev" ---08/30"><span style="font-size:10.0pt;color:#424282">"Sneed, Brandon via swift-corelibs-dev"
---08/30/2017 03:07:05 PM---Hi Tony, I like the idea that the type itself is responsible for the conversion. My own json encode</span><br>
<span style="font-size:10.0pt;color:#5F5F5F"><br>
From: </span><span style="font-size:10.0pt">"Sneed, Brandon via swift-corelibs-dev" <swift-corelibs-dev@swift.org><span style="color:#5F5F5F"><br>
To: </span>Tony Parker <anthony.parker@apple.com><span style="color:#5F5F5F"><br>
Cc: </span>"swift-corelibs-dev@swift.org" <swift-corelibs-dev@swift.org><span style="color:#5F5F5F"><br>
Date: </span>08/30/2017 03:07 PM<span style="color:#5F5F5F"><br>
Subject: </span>Re: [swift-corelibs-dev] Adding type conversion capabilities to JSON encode/decode<span style="color:#5F5F5F"><br>
Sent by: </span>swift-corelibs-dev-bounces@swift.org</span><o:p></o:p></p>
<div class="MsoNormal">
<hr size="2" width="100%" noshade="" style="color:#AAAAAA" align="left">
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<p class="MsoNormal"><br>
<br>
<br>
<br>
Hi Tony,<br>
<br>
I like the idea that the type itself is responsible for the conversion. My own json encode/decode library worked this way and it was really great, however in trying to leverage Swift4 into it, or to replace it, I just don’t see how that’s possible given how
it’s currently structured.<br>
<br>
JSON’s types effectively end up matching specifically to primitives, of which there is no mechanism to override the behavior of how a String gets decoded for instance. The only way I can think of to accomplish that is to create *<b>another</b>* type, JSONString
for example, but since String is a struct, I can’t subclass it, and instead need to have the real value buried inside of it … it seems to start getting messy very quickly. It also adds the obfuscation of dealing with yet another type, which I’m not against,
but just feels less than ideal.<br>
<br>
<br>
Brandon Sneed<br>
<b><br>
From: </b><anthony.parker@apple.com> on behalf of Tony Parker <anthony.parker@apple.com><b><br>
Date: </b>Wednesday, August 30, 2017 at 11:30 AM<b><br>
To: </b>"Sneed, Brandon" <brsneed@ebay.com><b><br>
Cc: </b>Itai Ferber <iferber@apple.com>, "swift-corelibs-dev@swift.org" <swift-corelibs-dev@swift.org><b><br>
Subject: </b>Re: [swift-corelibs-dev] Adding type conversion capabilities to JSON encode/decode<br>
<br>
I’m still not convinced that we should actually provide such a strategy. <br>
<br>
Conversions like those below seem like the domain of each type that is being decoded. If, in a particular type, the “number” can be either a true number or a string, then that type can try decoding it as one or the other and fall back as required. That puts
the responsibility of doing that kind of conversion in the type itself.<br>
<br>
JSON has very few types already. I’m not sure we want to blur the line between numbers and strings automatically…<br>
<br>
- Tony <o:p></o:p></p>
<p class="MsoNormal" style="margin-left:2.0in">On Aug 30, 2017, at 11:24 AM, Sneed, Brandon via swift-corelibs-dev <<a href="mailto:swift-corelibs-dev@swift.org">swift-corelibs-dev@swift.org</a>> wrote:<br>
<br>
Hi Itai,<br>
<br>
No problem! Thanks for the heads up. Is there any way I could be involved? Happy to do the work to whatever guidance your team might have. I’m mostly just interested in it being there soon, hence volunteering.
<br>
<br>
Thanks!<br>
<br>
<br>
Brandon Sneed<br>
<b><br>
From: </b><<a href="mailto:iferber@apple.com">iferber@apple.com</a>> on behalf of Itai Ferber <<a href="mailto:iferber@apple.com">iferber@apple.com</a>><b><br>
Date: </b>Wednesday, August 30, 2017 at 11:22 AM<b><br>
To: </b>"Sneed, Brandon" <<a href="mailto:brsneed@ebay.com">brsneed@ebay.com</a>><b><br>
Cc: </b>"<a href="mailto:swift-corelibs-dev@swift.org">swift-corelibs-dev@swift.org</a>" <<a href="mailto:swift-corelibs-dev@swift.org">swift-corelibs-dev@swift.org</a>><b><br>
Subject: </b>Re: [swift-corelibs-dev] Adding type conversion capabilities to JSON encode/decode<br>
<span style="font-family:Helvetica"><br>
Hi Brandon,<br>
Thanks for looking at this! We’ve got plans internally to potentially add a strategy to
</span><span style="font-size:10.0pt;font-family:"Courier New"">JSONEncoder</span><span style="font-family:Helvetica">/</span><span style="font-size:10.0pt;font-family:"Courier New"">JSONDecoder</span><span style="font-family:Helvetica"> to allow lenient conversions
like this — i.e. implicitly stringify numbers (or parse them from string input), among some others.<br>
This would be opt-in for consumers of </span><span style="font-size:10.0pt;font-family:"Courier New"">JSONDecoder</span><span style="font-family:Helvetica"> while not requiring any special annotations on
</span><span style="font-size:10.0pt;font-family:"Courier New"">Codable</span><span style="font-family:Helvetica"> types.<br>
— Itai<br>
On 30 Aug 2017, at 10:59, Sneed, Brandon via swift-corelibs-dev wrote:</span><span style="color:#777777"><br>
Hi everyone,</span><br>
<span style="color:#777777"><br>
Just throwing this out to see if anyone else is working on this, or has opinions/suggestions on how it’s implemented. I’d like to add this to the Codable/JSONDecoder/JSONEncoder system if no one else is working on it.</span><br>
<span style="color:#777777"><br>
Type type conversion, I mean given this JSON payload:</span><br>
<span style="color:#777777"><br>
{<br>
"name": "Endeavor”,<br>
"abv": 8.9,<br>
"brewery": "Saint Arnold”,<br>
"style": "ipa"<br>
}</span><br>
<span style="color:#777777"><br>
and a struct defined as:</span><br>
<span style="color:#777777"><br>
struct Beer: Codable {<br>
let name: String<br>
let abv: String<br>
let brewery: String<br>
let style: BeerStyle<br>
}</span><br>
<span style="color:#777777"><br>
Notice that “abv” is a number in the JSON, but a String in the struct. I’d like to make it such that I can let the system know it’s ok to convert it from a number to a string as opposed to throwing an exception. The benefits are:</span><br>
<span style="color:#777777"><br>
1. It’s defensive; service types can change without causing my application to crash.<br>
2. It allows a developer to work with the types they want to work with as opposed to what the server provides, thus saving them time of writing a custom encode/decode code for all members.</span><br>
<span style="color:#777777"><br>
The argument against it that I’ve heard is generally “it’s a service bug, make them fix it”, which is valid but the reality is we’re not all in control of the services we injest. The same type of logic could be applied to a member name changing, though I haven’t
seen this happen often in practice. I do see types in a json payload change with some frequency though. I think much of the reason stems from the fact that type conversion in javascript is effectively free, ie: you ask for a String, you get a String if possible.</span><br>
<span style="color:#777777"><br>
To implement this type conversion in practice, looking at it from the point of view using Codable/JSON(en/de)coder, one way would be to make it opt-in:</span><br>
<span style="color:#777777"><br>
struct Beer: Codable, CodingConvertible {<br>
let name: String<br>
let abv: String<br>
let brewery: String<br>
let style: BeerStyle<br>
}</span><br>
<span style="color:#777777"><br>
I like this because looking at the struct, the members still remain clear and relatively unambiguous. The downside is it’s unknown which member is likely to get converted. And since it’s opt-in, conversion doesn’t happen if the CodingConvertible conformance
isn’t adhered to.</span><br>
<span style="color:#777777"><br>
Another option would be to box each type, like so:</span><br>
<span style="color:#777777"><br>
struct Beer: Codable {<br>
let name: String<br>
let abv: Convertible<String><br>
let brewery: String<br>
let style: BeerStyle<br>
}</span><br>
<span style="color:#777777"><br>
This seems tedious for developers, but would show which types are being converted. It does however seriously weaken benefit #1 above.</span><br>
<span style="color:#777777"><br>
Those example usages above aside, I do think it’d be best if this conversion behavior was the default and no end-developer changes required. I think that could be done without impact to code that’s been already been written against the JSON en/decode bits.</span><br>
<span style="color:#777777"><br>
I’m very open to alternatives, other ideas, or anything else you might have to say on the subject. Thanks for reading!</span><br>
<br>
<br>
<span style="color:#777777"><br>
Brandon Sneed</span><br>
<br>
<br>
<br>
<span style="font-family:Helvetica;color:#777777"><br>
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