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From MG <mg...@arscreat.com>
Subject Groovy Name-and-Value Macro Support Proposal
Date Wed, 27 Jun 2018 19:10:47 GMT
Hi,

I have given Groovy 2.5's new macro support a spin and implemented 
functionality to support code constructs which I could last use with 
C++'s macro preprocessor stringify operation (and which I always found 
very helpful for debugging / creating runtime log output).

Example:

final ageOfTree =124 final towerHeight =987.654 final String visitorName ="abc" final s1 ="DEFGH"
final gs0 ="val0:$ageOfTree" final GString gs1 ="TheTower($towerHeight)" final List names
= ["Peter","Ann","Raymond" ]

println"single variables: ${NV(ageOfTree)}and ${NV(gs0)}and ${NV(visitorName)}and ${NV(s1)}and
${NV(gs1)}and also ${NV(names)})}" println"variable list: ${NVL(ageOfTree, gs0, visitorName,
s1, towerHeight, gs1, names)}"which prints: single variables: ageOfTree=124 and gs0="val0:124"
and 
visitorName="abc" and s1="DEFGH" and gs1="TheTower(987.654)" and also 
names=[Peter, Ann, Raymond])}variable list: [ageOfTree=124, 
gs0="val0:124", visitorName="abc", s1="DEFGH", towerHeight=987.654, 
gs1="TheTower(987.654)", names=[Peter, Ann, Raymond]]NV here is a Groovy 
macro method which, which allows turning the passed variable expression 
into its name and value in the form of a simple NameAndValue class 
instance. NVL does the same for multiple variables (returning a list of 
NameAndValue|s). (I used a different name for NVL, to allow for NV to 
take more than one variable expression parameter (and return e.g. a 
GString that contains a sequence of "name=$val" expressions without the 
enclosing list brackets), or to allow for NV to take additional 
parameters). Such an extension would be useful, because it:

 1. Reduces the amount of boilerplate code one needs to write
 2. Makes the code more concise
 3. Removes errors such as: println "var0=$var0, var1=$var0"

I therefore propose we add this functionality to Groovy 2.5.x . Apart 
from the general decision, open questions for me are:

 1. Where do we put macro extensions in the Groovy source code ?
 2. What names should we use for macro methods ?

I lean towards using C/C++ macro naming conventions as a guideline, i.e. 
using short, abbreviated, uppercase-only names such as NV = named 
variable, or NVL = named variable list, since:

 1. Macros allow for "magic" and are not really method calls in the
    classical sense
 2. Java do not have macros, so the hope would be that making them stick
    out a bit will make them less confusing for developers coming from
    Java to Groovy
 3. On the other hand C/C++ developers that are used to macros will
    immediately suspect that they are looking at a macro-like construct
 4. Independent of upper-/lowercase, brevity is important, especially
    for the proposed two NV/NVL macros, since it would imho be desirable
    for e.g. "NV(x)" to not take up more space than "x=$x"

In any case macro-method support in Groovy is a fantastic feature, which 
opens up completely new possibilities for language & framework 
developers - Go Groovy !-)
Please comment,
Cheers,
mg






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