Hi Sergei, ( Copied from twitter: https://twitter.com/bsideup/status/1287477595643289601?s=20 ) > But isn't it better with pattern matching? And what is "_" here? The underscore represents the return value
> Anyways: > ``` > return match (_) { > case { it < 5 }: callC(); > case { it > 10 }: callB(); > case { it != null }: callA(); > default: { > LOG.debug "returning callD" > return callD() > } > } > ``` pattern matching may cover some cases of Conditional Return, but it can not cover all. Actually the Conditional Return is more flexible, e.g. ``` def chooseMethod(String methodName, Object[] arguments) { return doChooseMethod(methodName, arguments) if _ != null for (Class type : [Character.TYPE, Integer.TYPE]) { return doChooseMethod(methodName, adjustArguments(arguments.clone(), type)) if _ != null } throw new GroovyRuntimeException("$methodName not found") } ``` Even we could simplify the above code with `return?` if the condition is Groovy truth: ``` def chooseMethod(String methodName, Object[] arguments) { return? doChooseMethod(methodName, arguments) for (Class type : [Character.TYPE, Integer.TYPE]) { return? doChooseMethod(methodName, adjustArguments(arguments.clone(), type)) } throw new GroovyRuntimeException("$methodName not found") } ``` Cheers, Daniel Sun On 2020/07/26 18:23:41, Daniel Sun <sun...@apache.org> wrote: > Hi mg, > > > maybe you can give some real life code where you encounter this on a > > regular basis ? > > Let's think about the case about choosing method by method name and arguments: > > ``` > def chooseMethod(String methodName, Object[] arguments) { > def methodChosen = doChooseMethod(methodName, arguments) > if (null != methodChosen) return methodChosen > > methodChosen = doChooseMethod(methodName, > adjustArguments(arguments.clone(), Character.TYPE)) > if (null != methodChosen) return methodChosen > > methodChosen = doChooseMethod(methodName, > adjustArguments(arguments.clone(), Integer.TYPE)) > if (null != methodChosen) return methodChosen > > throw new GroovyRuntimeException("$methodName not found") > } > ``` > > The above code could be simplified as: > ``` > def chooseMethod(String methodName, Object[] arguments) { > return? doChooseMethod(methodName, arguments) > > return? doChooseMethod(methodName, adjustArguments(arguments.clone(), > Character.TYPE)) > > return? doChooseMethod(methodName, adjustArguments(arguments.clone(), > Integer.TYPE)) > > throw new GroovyRuntimeException("$methodName not found") > } > ``` > > Or a general version: > ``` > def chooseMethod(String methodName, Object[] arguments) { > return doChooseMethod(methodName, arguments) if _ != null > > return doChooseMethod(methodName, adjustArguments(arguments.clone(), > Character.TYPE)) if _ != null > > return doChooseMethod(methodName, adjustArguments(arguments.clone(), > Integer.TYPE)) if _ != null > > throw new GroovyRuntimeException("$methodName not found") > } > ``` > > > Cheers, > Daniel Sun > On 2020/07/26 17:11:07, MG <mg...@arscreat.com> wrote: > > Hi Daniel, > > > > currently I would be +/- 0 on this. > > > > Thoughts: > > > > 1. I feel I have written this before, but I myself do not encounter the > > situation where I would need to return the result of a method call > > only if it meets certain conditions when programming (maybe you can > > give some real life code where you encounter this on a regular basis ?). > > 2. If I have more than one return, it typcially is an early out, which > > depends on the method's input parameters, not on the result of > > another method call. > > 3. Since I do a lot of logging / log debugging, I typically assign the > > return value to a variable, so I can debug-log it before the one > > return of the method. > > 4. In fact I have had to refactor code written by other people from > > multi-return methods to single return, to be able to track down bugs. > > > > So overall I am not sure one should enable people to make it easier to > > write non-single-return methods ;-) > > > > > > Purely syntax wise I would prefer > > return? > > for the simple case, > > > > and > > > > return <something> if <condition> > > for the more complex one*. > > > > I find > > return(<condition) <something> > > confusing on what is actually returned. > > > > Cheers, > > mg > > > > *Though I wonder if people would not then expect this if-postfix-syntax > > to also work for e.g. assignments and method calls... > > > > > > On 26/07/2020 16:15, Daniel Sun wrote: > > > Hi Mario, > > > > > > I think you have got the point of the proposal ;-) > > > > > > If we prefer the verbose but clear syntax, I think we could > > > introduce `_` to represent the return value for concise shape: > > > > > > ``` > > > return callB() if (_ != null && _ > 10) > > > > > > // The following code is like lambda expression, which is a bit more > > > verbose > > > return callB() if (result -> result != null && result > 10) > > > ``` > > > > > > Show the `_` usage in your example: > > > ``` > > > def doSomething(int a) { > > > return callB() if (a > 6 && _ > 10) > > > return callC() if (a > 5 && _ > 20) > > > return callD() if (a > 4 && _ > 30) > > > } > > > ``` > > > > > > ``` > > > // optional parentheses > > > def doSomething(int a) { > > > return callB() if a > 6 && _ > 10 > > > return callC() if a > 5 && _ > 20 > > > return callD() if a > 4 && _ > 30 > > > } > > > ``` > > > > > > ``` > > > // one more example > > > def doSomething(int a) { > > > return callB() if a > 6 && _ > 10 > > > return callC() + callD() if a > 5 && _ > 50 > > > } > > > ``` > > > > > > BTW, the parentheses behind `if` could be optional. > > > > > > Cheers, > > > Daniel Sun > > > On 2020/07/26 11:29:39, Mario Garcia <mario.g...@gmail.com> wrote: > > >> Hi all: > > >> > > >> Very interesting topic. > > >> > > >> The first idea sprang to mind was the PMD rule in Java saying you should > > >> have more than one exit point in your methods ( > > >> https://pmd.github.io/latest/pmd_rules_java_codestyle.html#onlyonereturn). > > >> But the reality is that sometimes (more often than not) we are forced to > > >> break that rule. In fact sometimes we could even argue that breaking that > > >> rule makes the code clearer (e.g > > >> https://medium.com/ncr-edinburgh/early-exit-c86d5f0698ba) > > >> > > >> Although my initial reaction was to be against the proposal, however > > >> after > > >> doing some coding, I've found that neither elvis nor ternary operators > > >> makes it easier nor clearer. Here's why I think so. Taking Daniel's > > >> example: > > >> > > >> ``` > > >> def m() { > > >> def a = callA() > > >> if (null != a) return a > > >> > > >> def b = callB() > > >> if (b > 10) return b > > >> > > >> def c = callC() > > >> if (null != c && c < 10) return c > > >> > > >> LOGGER.debug('the default value will be returned') > > >> > > >> return defaultValue > > >> } > > >> ``` > > >> The shortest elvis operator approach I could think of was: > > >> ``` > > >> def m2() { > > >> return callA() > > >> ?: callB().with { it > 10 ? it : null } > > >> ?: callC().with { null != it && it <10 ? it : null } > > >> } > > >> ``` > > >> > > >> which to be honest, is ugly to read, whereas Daniel's proposal is just: > > >> > > >> ``` > > >> def m() { > > >> return? callA() > > >> return(r -> r > 10) callB() > > >> return(r -> null != r && r < 10) callC() > > >> return defaultValue > > >> } > > >> ``` > > >> > > >> Once said that, I would say this conditional return could be useful only > > >> when there are more than two exit points, otherwise ternary or elvis > > >> operators may be good enough. > > >> > > >> So, bottom line, I kinda agree to add conditional return, but I'm not > > >> sure > > >> about the final syntax: > > >> > > >> ``` > > >> return(r -> r > 10) callB() > > >> return callB() [r -> r > 10] > > >> return callB() if (r -> r > 10) > > >> ``` > > >> > > >> Between the three I the one that I like the most is the third one: > > >> > > >> ``` > > >> return callB() if (r -> r > 10) > > >> ``` > > >> > > >> You can read it in plain english as "return this if this condition > > >> happens". > > >> > > >> Apart from Daniel's use case, using this option could open the > > >> possibility to use, not only a closure or lambda expression, but also a > > >> plain expression. A nice side effect could be that something like the > > >> following code: > > >> > > >> ``` > > >> def doSomething(int a) { > > >> return callB() if a > 6 > > >> return callC() if a > 5 > > >> return callD() if a > 4 > > >> } > > >> ``` > > >> > > >> turns out to be a shorter (and in my opinion nicest) way of switch case > > >> (when you want every branch to return something): > > >> > > >> ``` > > >> def doSomething(int a) { > > >> switch (a) { > > >> case { it > 6 }: return callB() > > >> case { it > 5 }: return callC() > > >> case { it > 4 }: return callD() > > >> } > > >> } > > >> ``` > > >> > > >> Well, bottom line, I'm +1 Daniel's proposal because I've seen some cases > > >> where this conditional return could make the code clearer. > > >> > > >> Cheers > > >> Mario > > >> > > >> El sáb., 25 jul. 2020 a las 23:55, Paolo Di Tommaso (< > > >> paolo.ditomm...@gmail.com>) escribió: > > >> > > >>> It's not much easier a conditional expression (or even the elvis > > >>> operator)? > > >>> > > >>> ``` > > >>> def m() { > > >>> def r = callSomeMethod() > > >>> return r != null ? r : theDefaultResult > > >>> } > > >>> ``` > > >>> > > >>> > > >>> On Sat, Jul 25, 2020 at 8:56 PM Daniel Sun <sun...@apache.org> wrote: > > >>> > > >>>> Hi all, > > >>>> > > >>>> We always have to check the returning value, if it match some > > >>>> condition, return it. How about simplifying it? Let's see an example: > > >>>> > > >>>> ``` > > >>>> def m() { > > >>>> def r = callSomeMethod() > > >>>> if (null != r) return r > > >>>> > > >>>> return theDefaultResult > > >>>> } > > >>>> ``` > > >>>> > > >>>> How about simplifying the above code as follows: > > >>>> ``` > > >>>> def m() { > > >>>> return? callSomeMethod() > > >>>> return theDefaultResult > > >>>> } > > >>>> ``` > > >>>> > > >>>> Futhermore, we could make the conditional return more general: > > >>>> ``` > > >>>> def m() { > > >>>> return(r -> r != null) callSomeMethod() // we could do more > > >>>> checking, > > >>>> e.g. r > 10 > > >>>> return theDefaultResult > > >>>> } > > >>>> ``` > > >>>> > > >>>> Any thoughts? > > >>>> > > >>>> Cheers, > > >>>> Daniel Sun > > >>>> > > > > >