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From MG <mg...@arscreat.com>
Subject Named Parameters Support
Date Sat, 22 Jul 2017 21:17:27 GMT
Hi,

having recently explained why Groovy is my language of choice got me 
thinking about the few areas of Groovy where I personally wish for / see 
the potential for improvement during my daily development tasks.

I will start off with named paramters support, a topic that has been 
moving more into my consciousness as the framework I develop at work 
grew larger over time: I feel that the current named parameter support I 
am aware of 
(http://groovy-lang.org/objectorientation.html#_named_argument_constructor 
/ http://groovy-lang.org/objectorientation.html#_named_arguments ) is a 
limited feature that fit relatively well with a purely dynamic language, 
but is not nearly as well rounded / powerful as in other languages.

Do you have any plans to support named parameters such as they exist 
e.g. in PL/SQL (to be honest, I never expected I would ever quote PL/SQL 
as a language that is superior to Groovy in any aspect before I thought 
about this ;-) ), where named paramters are just a convenient (and 
safer) way to call a callable, without loosing type safety, which works 
in a purely static manner, and without requiring a method to explicitely 
deal with a Map as its argument.
In short, a way to call any Groovy method/ctor with a syntax like:

class Processor {
     Processor(String name, boolean writeableQ = false, boolean 
extendableQ = true,  Number id = null, Worker defaultWorker = null, 
Closure logCls = {  println it }) { ... }
     work(Worker worker = null, boolean dryRunQ = false, int 
maxNrRetries = 10, boolean overwriteQ = false) { ... }
}

final processor= new Processor(name:"Task 1", id:1234) { log.debug "T1: 
$it" }  // Closure as last argument can still be given outside of brackets
processor.work(maxNrRetries:99)


The grooviest thing of all would be, if there would be a way to keep the 
flexibility of the map argument, and combine it with the named 
arguments, to be able to e.g. define a different default set of default 
values for a method/ctor. E.g.

static ParametersMap getDebugWorkParams() {
     return [ worker:dummyWorker, dryRunQ:true, maxNrRetries:0, 
overwriteQ:true ]
}

processor.work(*(debugWorkParams + [worker:logOnlyWorker, 
maxNrRetries:3])) // dryRunQ=true and overwriteQ=true comes from 
debugWorkParams; worker and maxNrRetries are give explicitly in call


In my case such a feature would have two benefits:
1a) Make it easy to quickly add a final field to a root base class, 
without having to do some a major ctor refactoring on all the child 
classes (for which I typically don't have the time, meaning that I am 
forced to add the field as non-final "for now", so I can modify it after 
object creation where needed).
Note that this can, even if IntelliJ would not sometimes not get the 
refactoring wrong (which can lead to hard to track bugs), not be covered 
by better refactoring support: Not having to give all the values for the 
parameters before the newly added parameter (but instead having them 
take their default value) is not something a refactoring engine can supply.
1b) Similar to 1a), for adding parameters to method calls
2) Make the calling of ctors/methods safer in certain cases
a) When a ctor/method takes a lot of parameters of the same type, e.g. 
boolean: createPackageSql(String name, boolean trimQ, boolean 
indentLinesQ, boolean keepEmptyLinesIndentationQ, boolean 
seperateFunctionsQ, boolean uppercaseKeywordsQ, boolean uppercaseNamesQ) 
{ ... } *
b) When a framework function is called by a framework user, e.g. from a 
script, or generally in an environment where there is little or no test 
coverage, and the paramter order can easily be confused: e.g. method 
which retrieves a DB item through 2 IDs, and getting an empty result set 
is not an error - which ID has to be given first ? Easy, when calling 
with named paramters is supported pe.retrieveTreeNodeRow(orgUnit:123, 
orgItem:456) .

mg

*Here a parameter object might be the better choice. But typically the 
number of paramters was small at the beginning, and grew over time, so 
initially no need for a paramater object existed. Again the refactoring 
time needed to introduce a parameter object, the fact that your class 
namespace gets cluttered with helper structures, external framework 
users will have to adapt their code (or you must maintain a backward 
compatibility facade), etc make this less practical than it might 
initially seem...




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