Scala反射：如何列出範圍內的所有變量？

Question

如何在範圍/環境/綁定中列出所有「變量」（不僅是變量）的名稱和/或值？我需要（1）生成一個列表或者（2）打印一個Scala可以訪問的所有實體的列表聲明。

Answer 1

在運行時這是不可能的 - 至少不是你想要的方式 - 因爲JVM沒有組織成每個語句後更新的符號的巨大表格，您可以隨時查詢並找到名稱爲的實體 ，就像你給他們打電話一樣（我認爲這是跨語言和環境的）。

您可以嘗試查詢確實組織爲表格的內容，例如類/接口的方法，但在之前您必須知道類別的完全限定名稱。爲了給你一個快速的例子，根據類加載的工作原理，JVM甚至無法枚舉你可以創建的類，因爲新的類可以實時創建或從某個存儲庫檢索。再舉一個例子，import在運行時不存在...

您必須縮小您的需求。例如，如果您定位REPL，那麼您可能會修改它以混淆其內部數據結構（但努力會很大）。類似地，如果你的目標是一個腳本並且有權訪問這些源代碼，那麼理論上你可以用一個插件來修改編譯器，它可以完成你所需要的工作。被警告我只提到這些事情，但不會考慮自己做這樣的事情，因爲這需要很大的努力，我看不到任何真正的需要。

Answer 2

的問題大致可以理解，但例如REPL有作用域綁定javax.script一些支持：

$ scala 
Welcome to Scala version 2.11.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_11). 
Type in expressions to have them evaluated. 
Type :help for more information. 

scala> val e = $intp.asInstanceOf[javax.script.ScriptEngine] 
e: javax.script.ScriptEngine = scala.tools.nsc.interpreter.ILoop$ILoopInterpreter@2b71fc7e 

scala> e.getContext 
res0: javax.script.ScriptContext = javax.script.SimpleScriptContext@63c12fb0 

scala> e.getContext.getScopes 
res1: java.util.List[Integer] = [100, 200] 

scala> e.getContext.getBindings(100) 
res2: javax.script.Bindings = {} 

而且REPL本身保持，可以進行查詢的範圍，表示當前的歷史被自動導入到腳本的當前行會話：

scala> $intp.replScope 
res3: $intp.global.Scope = Scopes(value $intp, value e, value res0, value res1, value res2) 

也有可能行使REPL的完成機制：

scala> :power 
** Power User mode enabled - BEEP WHIR GYVE ** 
** :phase has been set to 'typer'.   ** 
** scala.tools.nsc._ has been imported  ** 
** global._, definitions._ also imported ** 
** Try :help, :vals, power.<tab>   ** 

scala> reader.completion 
res4: scala.tools.nsc.interpreter.Completion = scala.tools.nsc.interpreter.JLineCompletion@68b7bdcb 

scala> res4.completer.complete("",0) 
res6: scala.tools.nsc.interpreter.Completion.Candidates = Candidates(0,List($intp, $ires0, $ires1, $ires10, $ires11, $ires12, $ires13, $ires14, $ires15, $ires16, $ires17, $ires18, $ires2, $ires3, $ires4, $ires5, $ires6, $ires7, $ires8, $ires9, $r, AND, BLOCK, CASE, DEFAULT, FALSE, IF, LIT, NEW, NOT, NULL, REF, SOME, SelectStart, TRUE, TRY, UNIT, ZERO, analyzer, classOf, completion, e, fn, global, history, intp, isettings, lastRequest, mkTreeFromSelectStart, mkTreeMethods, mkTreeMethodsFromSelectStart, mkTreeMethodsFromSymbol, nullSafe, phased, power, r, reader, repl, replImplicits, res0, res1, res2, res3, res4, returning, scala$tools$nsc$ast$TreeDSL$CODE$$$outer, treedsl, typed, typer, vals)) 

scala> 

在REPL控制檯的單一選項卡提供自動完成功能，在這裏顯示了我的當前目錄下所有的垃圾，這是在類路徑默認：

$ scala 
Welcome to Scala version 2.11.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_11). 
Type in expressions to have them evaluated. 
Type :help for more information. 

scala> 
$intp   broken   enumtest  inheritthewind maker   oracle  sbtbomb    thingy   
P    bumper   erased   inlined   mangled   orelse  scala    throwgen  
Q    butwhen   exh   inliner   mapeach   org   scallop    thrownull  
SO22581163  bytype   eyeshadow  inner   maqicode  othercase  scrap    tiles   
_root_   callbacks  fany   inputcheck  matchprim  out   scripts    timezone  
a    capture   featureless intcake   maybeamb  overdone  searchme   tmp    
abjectfuture cce    ff    interp   maykov   overnullary selfpub    toString  
absval   cdtest   fielding  interpat   metamac   pathmaker  seqto    tops   
adaptation  charmatch  filloval  intpbind   mkarray   peasy   serialmigration  trial   
akka   choosy   filrdr   intupolated  mksym   pet   serious    tribool   
algedu   classOf   findwidgets invokeFrom  modtest   petconfig  shapelessed   tricks   
angeldance  classmatch  finf   isInstanceOf  myanno   phyl   simple-swing  trivial   
annee   classy   fixedimp  isanon   mydays   pickit  singleton   tryxform  
annie   cmpprs   fixes   isfun   myintp   pimpin  slider    tstest   
annoconst  coltfred   fixme   isscala   mypkg   pkginvoke  slow    typeref   
annot   com    flib   java    mypriv   plugincp  smtest    tztest   
anymember  compilit   foodir   javafx   nestedmain  plugs   sobral    unapplynull  
anything  convprs   fooplus  javax   netscape  pointers  somatch    unavail   
applied  copier   for29   jbyte   newfrom   pointopt  some_package  unensured  
arrow   corner   formac   jdk    nextcompleted pos   sortitout   unused   
asInstanceOf counted   ftw   jex    niolock   poster  sounds    updater   
atrait   countints  funk   jext    noany   pow   specbug    valdef   
autoenum  cr    funkstr  jline   noapp   preferthunk speck    vec    
auxctor  ctag    futfilter  jmap    nodep   prettycase splitat    version   
bad-scales  curtest   futuremap  jover   nofeature  primover  stale    vowelshift  
badXlint  cyclic   fval   jperms   nofuture  printer  statik    w    
badaccess  dbadd   gline   junk    noimp   privctor  str2int    warnadapt  
badbob   default-tparam global   k    noinline  privover  strtyp    weakerr   
badgeneric  delayed   goodbye  kcharex   nointerp  procked  structural-return welper   
badimp   delayedsignal gr    keptstar   nonl   protcase  stupid    whose   
badinherit  delineate  grapher  kmap    norec   protval  succinctly   widgets   
badmap   demoapi   groupby  lazyparadox  nosehorn  publicity  sun     wrappedarray 
badmatch  dep    guiced   lazyside   nothingannot q    superduper   wtf    
badover  doc    guy   lazysplit  ns    qqparms  sxema    x    
badoverride dockable   halfinterval lib    nts    quickly  syncd    xmladd   
badpath  dosth   here   liner   nullgroup  quoterep  syshook    xmlex   
badpkg   doublearrow  hidden   linetest   nullpair  rawj   t1     xmlregex  
badseal  dummyonly  hiddenimport linted   nulltype  raws   t1807    xmlreplace  
badstrimp  dynospec   id    linty   nummaker  reader  t5148    xmlsub   
badvargs  earlier   imparted  lit    off    reflectenum t5589    xmlt   
badvol   eatery   imparter  littlecake  oiler5   replslow  t7121    xxx    
bigmethod  email   impctx   looker   old-and-blue repro   t7775    zed    
binder   empty   impless  lookit   oldname   required  t8433        
biterpolator emptypackage  impmag   lookup   om    sample-foo tabpane        
blocking  enclosing  imptest  loopy   oneq   samplewarn taggedparam       
blownfuture enclosingcls  imptrait  macinfer   oops   saver   target        
bounded  enpatch   include  macvar   optdate   sbt-test  teachers       

scala>