Scala反射：如何列出范圍內的所有變量？

Question

如何在范圍/環境/綁定中列出所有“變量”（不僅僅是變量）的名稱和/或值？

為了澄清，在程序/腳本的中間或在REPL的某個點，我需要（1）生成列表或（2）打印可由Scala語句訪問的所有實體的列表。

Answer 1

這個問題可以被廣泛地解釋，但是例如REPL對帶有作用域綁定的javax.script有一些支持：

$ 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 = {}

REPL本身保留了一個可以查詢的范圍，表示當前會話的歷史記錄，該歷史記錄自動導入當前腳本行：

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

也可以使用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> 

REPL控制台中的單個選項卡提供自動完成功能，此處顯示當前目錄中的所有垃圾，默認情況下位於類路徑上：

$ 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> 

Answer 2

這在運行時是不可能的 - 至少不是你想要的方式 - 因為JVM沒有被組織為在每個語句之后更新的巨大符號表，你可以隨時查詢並找到命名實體 ，就像你調用它們一樣（我認為這在語言和環境中都是如此）。

您可以嘗試查詢確實組織為表的內容，例如類/接口的方法，但在進行查詢之前必須知道類的完全限定名稱。 為了給您一個快速示例，根據類加載的工作原理，JVM甚至無法枚舉您可以創建的類，因為新的可以動態創建或從某個存儲庫中檢索。 再舉一個例子， import在運行時甚至不存在......

你必須縮小你的要求。 例如，如果您定位REPL，您可能（但努力將是巨大的）修改它以便混亂其內部數據結構。 類似地，如果您定位腳本並且可以訪問源代碼，理論上您可以使用插件來修改編譯器，從而完成所需的工作。 請注意，我只提到了這些東西，但從不考慮自己做這樣的事情，因為這需要付出很多努力，我看不出任何真正的需要。