I see where you're coming from.<br>Without any actual insight into the design of this syntax, I think throws is in the position it is because it relates more to the return type of the function. Aka a `throws -> T` function can either throw ErrorProtocol OR return a T value. <br><div class="gmail_quote"><div dir="ltr">On Tue, Jul 19, 2016 at 10:51 AM Matthieu Oger via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div><div>Hello,<br></div>
<div> </div>
<div>I'm currently reading the updated Swift 3 preview book, and was wondering about the `throws` and `rethrows` keywords.<br></div>
<div> </div>
<div>In a function declaration, all the keywords are at the beginning, except for `throws` and `rethrows`, which are… oddly placed.<br></div>
<div> </div>
<div>In the grammar:<br></div>
<div> </div>
<div>```<br></div>
<div style="border:0px;font-size:14px;margin:0px 0px 12px;outline:0px;padding:0px;vertical-align:baseline;background:transparent"><p style="border:0px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;background-image:initial;background-position:initial;background-repeat:initial"><span style="background-color:transparent"><span style="background-color:transparent"><span style="color:rgb(128,128,128)"><i><span style="font-size:10px">function-declaration</span><span><span style="font-size:10px"> </span></span></i><span style="font-size:10px">→</span><span><span style="font-size:10px"> </span></span></span><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-head" target="_blank"><span style="font-size:10px">function-head</span></a><span style="font-size:10px"> </span><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-name" target="_blank"><span style="font-size:10px">function-name</span></a><span style="font-size:10px"> </span></i><span style="background-color:transparent"><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/GenericParametersAndArguments.html#//apple_ref/swift/grammar/generic-parameter-clause" target="_blank"><span style="font-size:10px">generic-parameter-clause</span></a><span style="font-size:10px"></span></i></span><sub style="border:0px;font-size:0.8em;outline:0px;padding:0px 4px 0px 0px;vertical-align:sub;color:rgb(128,128,128);font-style:italic;background:transparent"><span style="font-size:10px">opt</span></sub><span style="font-size:10px"></span><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-signature" target="_blank"><span style="font-size:10px">function-signature</span></a><span style="font-size:10px"> </span></i><span style="background-color:transparent"><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-body" target="_blank"><span style="font-size:10px">function-body</span></a><span style="font-size:10px"></span></i></span><sub style="border:0px;font-size:0.8em;outline:0px;padding:0px 4px 0px 0px;vertical-align:sub;color:rgb(128,128,128);font-style:italic;background:transparent"><span style="font-size:10px">opt</span></sub><span style="font-size:10px"></span></span></span><span style="font-size:10px"><br></span></p></div>
<div style="border:0px;font-size:14px;margin:0px 0px 12px;outline:0px;padding:0px;vertical-align:baseline;background:transparent"><p style="border:0px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;background-image:initial;background-position:initial;background-repeat:initial"><span style="background-color:transparent"><span style="background-color:transparent"><span style="color:rgb(128,128,128)"><i><span style="font-size:10px">function-head</span><span><span style="font-size:10px"> </span></span></i><span style="font-size:10px">→</span><span><span style="font-size:10px"> </span></span></span><span style="background-color:transparent"><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Attributes.html#//apple_ref/swift/grammar/attributes" target="_blank"><span style="font-size:10px">attributes</span></a><span style="font-size:10px"></span></i></span><sub style="border:0px;font-size:0.8em;outline:0px;padding:0px 4px 0px 0px;vertical-align:sub;color:rgb(128,128,128);font-style:italic;background:transparent"><span style="font-size:10px">opt</span></sub><span style="font-size:10px"></span><span style="background-color:transparent"><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/declaration-modifiers" target="_blank"><span style="font-size:10px">declaration-modifiers</span></a><span style="font-size:10px"></span></i></span><sub style="border:0px;font-size:0.8em;outline:0px;padding:0px 4px 0px 0px;vertical-align:sub;color:rgb(128,128,128);font-style:italic;background:transparent"><span style="font-size:10px">opt</span></sub><span style="font-size:10px"></span></span><code style="border:0px;font-size:0.86em;margin:0px;outline:0px;padding:0px 4px;vertical-align:baseline;color:rgb(0,0,0);font-family:Menlo,monospace;font-weight:600;word-wrap:break-word;background:transparent"><span style="font-size:10px">func</span></code></span><span style="font-size:10px"><br></span></p><p style="border:0px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;background-image:initial;background-position:initial;background-repeat:initial"><span style="background-color:transparent"><span style="background-color:transparent"><span style="color:rgb(128,128,128)"><i><span style="font-size:10px">function-signature</span><span><span style="font-size:10px"> </span></span></i><span style="font-size:10px">→</span><span><span style="font-size:10px"> </span></span></span><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause" target="_blank"><span style="font-size:10px">parameter-clause</span></a><span style="font-size:10px"></span></i><code style="border:0px;font-size:0.86em;margin:0px;outline:0px;padding:0px 4px;vertical-align:baseline;color:rgb(0,0,0);font-family:Menlo,monospace;font-weight:600;word-wrap:break-word;background:transparent"><span style="font-size:10px">throws</span></code><sub style="border:0px;font-size:0.8em;outline:0px;padding:0px 4px 0px 0px;vertical-align:sub;color:rgb(128,128,128);font-style:italic;background:transparent"><span style="font-size:10px">opt</span></sub><span style="font-size:10px"></span><span style="background-color:transparent"><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-result" target="_blank"><span style="font-size:10px">function-result</span></a><span style="font-size:10px"></span></i></span><sub style="border:0px;font-size:0.8em;outline:0px;padding:0px 4px 0px 0px;vertical-align:sub;color:rgb(128,128,128);font-style:italic;background:transparent"><span style="font-size:10px">opt</span></sub><span style="font-size:10px"></span></span></span><span style="font-size:10px"><br></span></p><p style="border:0px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;background-image:initial;background-position:initial;background-repeat:initial"><span style="background-color:transparent"><span style="background-color:transparent"><span style="color:rgb(128,128,128)"><i><span style="font-size:10px">function-signature</span><span><span style="font-size:10px"> </span></span></i><span style="font-size:10px">→</span><span><span style="font-size:10px"> </span></span></span><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/parameter-clause" target="_blank"><span style="font-size:10px">parameter-clause</span></a><span style="font-size:10px"></span></i></span><code style="border:0px;font-size:0.86em;margin:0px;outline:0px;padding:0px 4px;vertical-align:baseline;color:rgb(0,0,0);font-family:Menlo,monospace;font-weight:600;word-wrap:break-word;background:transparent"><span style="font-size:10px">rethrows</span></code><span style="background-color:transparent"><span style="background-color:transparent"><i><a style="border:0px;font-size:14px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;color:rgb(0,136,204);text-decoration:none;background:transparent" href="https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/function-result" target="_blank"><span style="font-size:10px">function-result</span></a><span style="font-size:10px"></span></i></span><sub style="border:0px;font-size:0.8em;outline:0px;padding:0px 4px 0px 0px;vertical-align:sub;color:rgb(128,128,128);font-style:italic;background:transparent"><span style="font-size:10px">opt</span></sub><span style="font-size:10px"></span></span></span><br></p><p style="border:0px;margin:0px;outline:0px;padding:0px;vertical-align:baseline;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;line-height:20.3px;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;background-image:initial;background-position:initial;background-repeat:initial">```<br></p></div>
<div>Is there a reason to have throws and rethrows at this specific position, instead of declaration-modifiers?<br></div>
<div> </div>
<div>ie.:<br></div>
<div> </div>
<div>This:<br></div>
<div> </div>
<div>```<br></div>
<div><span style="background-color:rgb(255,255,255)"><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">func</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(121,93,163)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">send</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">() throws </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">-></span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(0,134,179)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">String</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> {}</span></span></span></span><br></div>
<div>```<br></div>
<div> </div>
<div>Becomes:<br></div>
<div> </div>
<div>```<br></div>
<div><span style="background-color:rgb(255,255,255)"><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">throwing </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">func</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(121,93,163)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">send</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">() </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">-></span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(0,134,179)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">String</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> {}</span></span></span></span><br></div>
<div><span style="background-color:rgb(255,255,255)"><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">rethrowing </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">func</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(121,93,163)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">send</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">() </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">-></span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(0,134,179)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">String</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> {}</span></span></span></span></span></span></span><br></div>
<div>```<br></div>
<div> </div>
<div>Like:<br></div>
<div> </div>
<div>```<br></div>
<div><span style="background-color:rgb(255,255,255)"><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">mutating</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">func</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(121,93,163)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">send</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">() </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">-></span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(0,134,179)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">String</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> {}</span></span></span></span><br></div>
<div>```<br></div>
<div> </div>
<div>Or:<br></div>
<div> </div>
<div>```<br></div>
<div><span style="background-color:rgb(255,255,255)"><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">throw </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">func</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(121,93,163)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">send</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">() </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">-></span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(0,134,179)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">String</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> {}</span></span></span></span><br></div>
<div><span style="background-color:rgb(255,255,255)"><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">rethrow </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">func</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(121,93,163)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">send</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">() </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">-></span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(0,134,179)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">String</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> {}</span></span></span></span></span></span></span><br></div>
<div>```<br></div>
<div> </div>
<div>Like: <br></div>
<div> </div>
<div>```<br></div>
<div><span style="background-color:rgb(255,255,255)"><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">override</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">func</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(121,93,163)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">send</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">() </span></span></span><span style="color:rgb(167,29,93)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">-></span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> </span></span></span><span style="color:rgb(0,134,179)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px">String</span></span></span><span style="color:rgb(51,51,51)"><span style="font-family:Consolas,"Liberation Mono",Menlo,Courier,monospace"><span style="font-size:12px"> {}</span></span></span></span><br></div>
<div>```<br></div>
<div> </div>
<div>(You can also see the weird difference between `override` and `mutating`, one using the -ing suffix, the other being infinitive) <br></div>
<div> </div>
<div>Am I missing something? I find that these keywords break the flow of the function declaration, separating the parameters and the return type, which is never done anywhere else.<br></div>
<div><div> </div>
<div>Thanks.</div>
<div> </div>
<div>--<br></div>
<div>Matthieu Oger<br></div>
<div><a href="http://pixelnest.io/" target="_blank">Pixelnest Studio</a><br></div>
</div>
<div> </div>
</div>
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</blockquote></div><div dir="ltr">-- <br></div><div data-smartmail="gmail_signature"><div dir="ltr">Javier Soto</div></div>