lucid.mind contemplative reflection for the jvm

Author: Chris Zheng  (
Date: 29 June 2017
Version: 1.3.13

1    Introduction

lucid.mind gives greater understanding of objects by providing a macro language on top of hara.reflect such that object introspection becomes very easy when working with the jvm. This library was originally iroh and then vinyasa.reflection.

1.1    Installation

Add to project.clj dependencies:

[im.chit/lucid.mind "1.3.13"]

All functionality is in the lucid.mind namespace:

(use 'lucid.mind)

1.2    Motivation

The words everything is data are taken literally when using lucid.mind to explore the world beyond clojure. Although functional programming have influenced the direction of Java as a whole, the object-orientated paradigm has a very deep hold on the language.

One OO paradigm - that of encapsulation - has been turned on it's head. In OO, it is a feature, in FP, it is a hinderence. lucid.mind bridges this gap. Taking inspiration from clj-wallhack, here are some primary use cases for the library:

  • To explore the members of classes as well as all instances within the repl
  • To be able to test methods and functions that are usually not testable, or very hard to test:
    • Make hidden class members visible by providing access to private methods and fields
    • Make immutable class members flexible for initialisation of state
  • Extract out class members into documented and executable functions (including multi-argument functions)
  • Better understand jvm security and how to dodge it if needed
  • Better understand the java type system as well as clojure's own interface definitions
  • To make working with java fun and informative

2    API

.% ^

lists class information

v 1.2
(defmacro .%
  `(reflect/class-info ~obj))
(.% String) => (contains {:modifiers #{:instance :public :final :class}, :name "java.lang.String"})

.%> ^

lists the class and interface hierarchy for the class

v 1.2
(defmacro .%>
  `(reflect/class-hierarchy ~obj))
(.%> String) => [java.lang.String [java.lang.Object #{ java.lang.Comparable java.lang.CharSequence}]]

.& ^

allow transparent field access and manipulation to the underlying object.

v 1.2
(defmacro .&
  `(reflect/delegate ~obj))
(def a "hello") (def >a (.& a)) (keys >a) => (contains [:hash]) (do (>a :value (char-array "world")) a) => "world"

.* ^

lists what methods could be applied to a particular instance

v 1.2
(defmacro .*
  [obj & selectors]
  `(reflect/query-instance ~obj ~(args/args-convert selectors)))
(.* "abc" :name #"^to") => ["toCharArray" "toLowerCase" "toString" "toUpperCase"] (.* String :name #"^to") => (contains ["toString"])

.> ^

threads the first input into the rest of the functions. Same as `->` but allows access to private fields using both `:keyword` and `.symbol` lookup:

v 1.2
(defmacro .>
  ([obj] obj)
  ([obj method]
   (cond (not (list? method))
         `(.> ~obj (~method))

         (list? method)
         (let [[method & args] method]
           (cond (#{'.* '.? '.% '.%> '.&} method)
                 `(~(symbol (str "vinyasa.reflection/" method)) ~obj ~@args)

                 (and (symbol? method) (.startsWith (name method) "."))
                 `(reflect/apply-element ~obj ~(subs (name method) 1) ~(vec args))

                 (keyword? method)
                 `(or (~method ~obj ~@args)
                      (let [nm# ~(subs (str method) 1)]
                        (if (some #(= % nm#) (reflect/query-instance ~obj [:name]))
                          (reflect/apply-element ~obj nm# ~(vec args)))))

                 `(~method ~obj ~@args)))))

  ([obj method & more]
   `(.> (.> ~obj ~method) ~@more)))
(.> "abcd" :value String.) => "abcd" (.> "abcd" .value String.) => "abcd" (let [a "hello" _ (.> a (.value (char-array "world")))] a) => "world"

.>ns ^

extracts all class methods into its own namespace.

v 1.2
(defmacro .>ns
  [ns class & selectors]
  `(reflect/extract-to-ns ~(list `symbol (str ns)) ~class ~(args/args-convert selectors)))
(map #(.sym %) (.>ns test.string String :private #"serial")) => '[serialPersistentFields serialVersionUID]

.>var ^

extracts a class method into a namespace.

v 1.2
(defmacro .>var
  ([name [class method & selectors]]
   `(reflect/extract-to-var ~(list `symbol (str name)) ~class ~(str method) ~(args/args-convert selectors)))
  ([name objvec & more]
   `[(.>var ~name ~objvec)
     ~@(map #(cons `.>var %) (partition 2 more))]))
(.>var hash-without [clojure.lang.IPersistentMap without]) (->> (eval '(clojure.repl/doc hash-without)) with-out-str string/split-lines (drop 2)) => ["[[clojure.lang.IPersistentMap java.lang.Object]]" " " "member: clojure.lang.IPersistentMap/without" "type: clojure.lang.IPersistentMap" "modifiers: instance, method, public, abstract"] (eval '(hash-without {:a 1 :b 2} :a)) => {:b 2}

.? ^

queries the java view of the class declaration

v 1.2
(defmacro .?
  [obj & selectors]
  `(reflect/query-class ~obj ~(args/args-convert selectors)))
(.? String #"^c" :name) => ["charAt" "checkBounds" "codePointAt" "codePointBefore" "codePointCount" "compareTo" "compareToIgnoreCase" "concat" "contains" "contentEquals" "copyValueOf"]

3    Fields

3.1    delegate

.& does what bean does but it actually allows field access to the underlying object through reflection. This way, one can set and get values from any object, regardless of permission model (private, protected, etc...).

First we create a string:

(def a "hello")
a => "hello"

Then we create the delegate for the string

(def >a (.& a))

;;=> <java.lang.String@99162322 {:hash 99162322, :hash32 0, :value #<char[] [C@202cf33f>}>

We can dereference the delegate to get the underlying fields of the object

@>a          ;;=> {:hash 99162322, :hash32 0, :value #<char[] [C@202cf33f>}

(keys >a)    ;;=> (:value :hash :hash32)

The delegate behaves exactly like a map:

(>a :hash)   ;;=> 99162322

(:hash32 >a) ;;=> 0

The value of the string a can also be changed through it's delegate >a, even though value is a private, final field:

(>a :value (char-array "world")) ;;=> "world"

a => "world"

3.2    class threading

.> is a convenience macro for accessing the innards of an object. It is akin to the threading -> macro except that now private fields can also be accessed:

(.> "hello" (:value) seq)
=> [\h \e \l \l \o]

changing the value of the string

(.> "hello" (:value "world") (:value) seq)
=> [\w \o \r \l \d]

4    Classes

4.1    class info

.% shows the infomation about a particular class or class instance:

(.% String)
=> (contains {:name "java.lang.String",
              :hash number?
              :modifiers #{:instance :public :final :class}})

This can also be used on a class instance itself:

(.% "abc")
=> {:name "java.lang.String",
    :hash 206835546,
    :modifiers #{:instance :public :final :class}}

4.2    class hierarchy

.%> shows the class hierarchy for a particular class or class instance:

(.%> 1)
=> [java.lang.Long
    [java.lang.Number #{java.lang.Comparable}]
    [java.lang.Object #{}]]

To read this, the first entry java.lang.Long is the actual type of the object. It extends java.lang.Number and implements the java.lang.Comparable interface. java.lang.Number extends java.lang.Object and implements the interface. So we can see the entire inheritance structure for the input 1.

A additional example is for a string:

(.%> "hello")
=> [java.lang.String
    [java.lang.Object #{java.lang.CharSequence

And for a clojure map:

(.%> {})
=> [clojure.lang.PersistentArrayMap
    [clojure.lang.APersistentMap #{clojure.lang.IKVReduce
    [clojure.lang.AFn #{java.util.Map
    [java.lang.Object #{clojure.lang.IFn}]]

As you can see, a map is not that simple.

5    Queries

5.1    class query

.? is used to list all methods belonging to a single class:

(.? 1)
;; (#[BYTES :: <java.lang.Long> | int]
;;  #[MAX_VALUE :: <java.lang.Long> | long]
;;  #[MIN_VALUE :: <java.lang.Long> | long]
;;  ...
;;  ...
;;  #[toUnsignedString :: (long) -> java.lang.String]
;;  #[toUnsignedString0 :: (long, int) -> java.lang.String]
;;  #[value :: (java.lang.Long) | long]
;;  #[valueOf :: (java.lang.String, int) -> java.lang.Long]
;;  #[valueOf :: (long) -> java.lang.Long]
;;  #[valueOf :: (java.lang.String) -> java.lang.Long])

It's not that useful to just return a whole bunch of elements and so the query is customizable through are many filters that can be used.

5.2    filter on name

The function name can be matched using either a string for exact match or a regex pattern for fuzzy match. To find all elements called valueOf, a string is used as input:

(.? 1 "valueOf")
;; (#[valueOf :: (java.lang.String, int) -> java.lang.Long]
;;  #[valueOf :: (long) -> java.lang.Long]
;;  #[valueOf :: (java.lang.String) -> java.lang.Long])

To find all elements starting with the letter c a regex can be constructed:

(.? 1 #"^c")
;; (#[compare :: (long, long) -> int]
;;  #[compareTo :: (java.lang.Long, java.lang.Object) -> int]
;;  #[compareTo :: (java.lang.Long, java.lang.Long) -> int]
;;  #[compareUnsigned :: (long, long) -> int])

5.3    elements

The query returns a list of elements. Each single element can be further explored. A query looking for methods named parselong yields two methods:

(.? 1 "parseLong")
;; (#[parseLong :: (java.lang.String, int) -> long]
;;  #[parseLong :: (java.lang.String) -> long])

The element can be captured to a variable.

(def parse-long (.? 1 "parseLong" :#))

Printing out the variable sees that it is a method that takes a string as input as returns a long.

(str parse-long)
=> "#[parseLong :: ([java.lang.String int]), ([java.lang.String])]"

The variable can used like any other clojure method:

(parse-long "202")
=> 202

Introspection of the element reveals that it indeed extends IFn and ILookup:

(.%> parse-long)
=> [hara.reflect.types.element.Element
    [java.lang.Object #{clojure.lang.IType

parse-long contains a lot more information that allows for it to behave like a typed function. The keyword :all accesses the data for the element:

(:all parse-long)
;; {:tag :multi,
;;  :name "parseLong",
;;  :array [#[parseLong :: (java.lang.String, int) -> long]
;;          #[parseLong :: (java.lang.String) -> long]],
;;  :lookup {:method {2 {[java.lang.String int]
;;                       #[parseLong :: (java.lang.String, int) -> long]},
;;                    1 {[java.lang.String]
;;                       #[parseLong :: (java.lang.String) -> long]}}},
;;  :cache #atom[{} 0x24ae0bde]}

Individual attributes are accessible through keyword lookup:

(:name parse-long)
=> "parseLong"

5.4    selection

Queries can be made with specific attribues returned, instead of the entire element by specifying options:

(.? 1 #"^parse" :name)
=> ("parseLong" "parseUnsignedLong")

(.? 1 #"^parse" :name :params)
=> ({:name "parseLong", :params [java.lang.String int]}
    {:name "parseLong", :params [java.lang.String]}
    {:name "parseUnsignedLong", :params [java.lang.String int]}
    {:name "parseUnsignedLong", :params [java.lang.String]})

The most useful keyword is :name as it provides a succinct way of listing the contents of a class:

(.? 1 :name)
    "TYPE" "bitCount" "byteValue" "compare"
    "compareTo" "compareUnsigned" "decode"
    "divideUnsigned" "doubleValue" "equals"
    "floatValue" "formatUnsignedLong" "getChars"
    "getLong" "hashCode" "highestOneBit"
    "intValue" "longValue" "lowestOneBit"
    "max" "min" "new" "numberOfLeadingZeros"
    "numberOfTrailingZeros" "parseLong"
    "parseUnsignedLong" "remainderUnsigned"
    "reverse" "reverseBytes" "rotateLeft"
    "rotateRight" "serialVersionUID" "shortValue"
    "signum" "stringSize" "sum" "toBinaryString"
    "toHexString" "toOctalString" "toString"
    "toUnsignedBigInteger" "toUnsignedString"
    "toUnsignedString0" "value" "valueOf"]

5.5    filter on modifiers

There are a list of modifiers that can be used for filtering:

(def flags
  [;; Element Type

   ;; Element Encapsulation

   ;; Element Attributes

For example, listing all the private fields of a string:

(.? String :name :private :field)
=> ("hash" "serialPersistentFields" "serialVersionUID" "value")

All static methods of String:

(.? String :name :method :static)
=> ("checkBounds" "copyValueOf" "format" "indexOf" "join" "lastIndexOf" "valueOf")

All the private non-static field names in String:

(.? String :name :private :field :instance)
=> ["hash" "value"]

5.6    multiselect

Going back to parseLong, it can be seen that there are two methods listed

(.? 1 "parseLong")
;; (#[parseLong :: (java.lang.String, int) -> long]
;;  #[parseLong :: (java.lang.String) -> long])

In order to get all of them under the same name, use :#

(.? 1 "parseLong" :#)
;; #[parseLong :: ([java.lang.String int]), ([java.lang.String])]

The type signature can take two types of inputs, as seen below:

(def parse-long-multi (.? 1 "parseLong" :#))
(parse-long-multi "10")
=> 10
(parse-long-multi "10" 10)
=> 10
(parse-long-multi "10" 2)
=> 2

This is very useful for including a bunch of methods

5.7    filter on signatures

The signature of methods can also be explored. A list of the name and params of methods starting with s that have 3 inputs are shown below:

(.? String :name :params #"^s" 3)
=> ({:name "split",
     :params [java.lang.String java.lang.String int]}
    {:name "startsWith",
     :params [java.lang.String java.lang.String int]}
    {:name "subSequence",
     :params [java.lang.String int int]}
    {:name "substring",
     :params [java.lang.String int int]})

The return type can be filtered by specifying a class. A list of methods that return a java.lang.String object are shown below:

(.? String :name String)
=> ("concat" "copyValueOf" "format" "intern"
    "join" "new" "replace" "replaceAll"
    "replaceFirst" "substring" "toLowerCase"
    "toString" "toUpperCase" "trim" "valueOf")

Input types can also be filtered by specifing an array with the type signature. A list of methods that take a java.lang.String as input are shown below:

(.? String :name :method [String])
=> ("getBytes" "hashCode" "intern" "isEmpty"
    "length" "toCharArray" "toLowerCase"
    "toString" "toUpperCase" "trim")

Match for any public method that contains an int in the input signature:

(.? String :name :public :method [:any int])
=> ("charAt" "codePointAt" "codePointBefore"
    "codePointCount" "copyValueOf" "getBytes"
    "getChars" "indexOf" "lastIndexOf"
    "offsetByCodePoints" "regionMatches"
    "split" "startsWith" "subSequence"
    "substring" "valueOf")

5.8    instance query

.* is very similar to .? in that it also inspects a variable and they have the same listing and filtering mechanisms. However, .? holds the java view of the Class declaration, staying true to the class and its members. .* holds the runtime view of Objects and what methods could be applied to that instance. .* will also look up the inheritance tree to fill in additional functionality.

Below shows the difference when asking for members of String beginning with c.:

(.? String  #"^c" :name)
=> ("charAt" "checkBounds" "codePointAt" "codePointBefore"
    "codePointCount" "compareTo" "compareToIgnoreCase"
    "concat" "contains" "contentEquals" "copyValueOf")
(.* String #"^c" :name)
=> ("cachedConstructor" "cannotCastMsg" "casAnnotationType"
    "cast" "checkBounds" "checkMemberAccess" "checkPackageAccess"
    "classRedefinedCount" "classValueMap" "clone"
    "copyValueOf" "createAnnotationData")

.? lists is what we expect when we read the documentation on java.lang.String. .* lists all static methods and fields as well as Class methods of String, whilst for instances of String, it will list all the instance methods from the entire class hierachy.

A further comparison can be seen when listing the public methods:

(.? {} :name :method :public)
=> ("asTransient" "assoc" "assocEx" "capacity" "containsKey"
    "count" "create" "createAsIfByAssoc" "createWithCheck"
    "empty" "entryAt" "iterator" "keyIterator" "kvreduce"
    "meta" "seq" "valAt" "valIterator" "withMeta" "without")
(.* {} :name :method :public)
=> ("applyTo" "asTransient" "assoc" "assocEx" "call" "capacity"
    "clear" "cons" "containsKey" "containsValue" "count" "empty"
    "entryAt" "entrySet" "equals" "equiv" "get" "getClass" "hashCode"
    "hasheq" "invoke" "isEmpty" "iterator" "keyIterator" "keySet"
    "kvreduce" "meta" "notify" "notifyAll" "put" "putAll" "remove"
    "run" "seq" "size" "throwArity" "toString" "valAt" "valIterator"
    "values" "wait" "withMeta" "without")

.? lists only the class declarations whereas .* lists all methods available to the instance, including methods from further up the inheritance tree. It can be said that the difference between the two is that .? takes the class view, whereas .* takes the runtime view.

6    Import

6.1    import as var

We can extract methods from a Class or interface with .>var:

(.>var hash-without [clojure.lang.IPersistentMap without]
       hash-assoc [clojure.lang.IPersistentMap assoc])
=> [#'documentation.lucid-mind/hash-without
(clojure.repl/doc hash-without)
;; documentation.lucid-mind/hash-without
;; [[clojure.lang.PersistentArrayMap java.lang.Object]]
;; member: clojure.lang.PersistentArrayMap/without
;; type: clojure.lang.IPersistentMap
;; modifiers: instance, method, public

(hash-without {:a 1 :b 2} :a)
=> {:b 2}
(clojure.repl/doc hash-assoc)
;; documentation.lucid-mind/hash-assoc
;; [[clojure.lang.IPersistentMap java.lang.Object java.lang.Object]]
;; member: clojure.lang.IPersistentMap/assoc
;; type: clojure.lang.IPersistentMap
;; modifiers: instance, method, public, abstract

(hash-assoc {:a 1 :b 2} :c 3)
=> {:a 1, :b 2, :c 3}

6.2    import as namespace

We can extract an entire class into a namespace. These are modifiable by selectors from .?. This is very useful for exploring a class by dumping out the contents into a test namespace:

(.>ns test.string String :public #"^c" 2)
=> (#'test.string/charAt
(str test.string/concat)
=> "#[concat :: (java.lang.String, java.lang.String) -> java.lang.String]"
(test.string/concat "hello " "world")
=> "hello world"