3 Examples top

• link | changes

  ;; Note that even though println returns nil, doto still returns the date object
  user> (doto (java.util.HashMap.)
              (.put "a" 1)
              (.put "b" 2)
              (println :printed))
  #<HashMap {b=2, a=1}> :printed
  #<HashMap {b=2, a=1}>

  ;; Note that even though println returns nil, doto still returns the date object user> (doto (java.util.HashMap.) (.put "a" 1) (.put "b" 2) (println :printed)) #<HashMap {b=2, a=1}> :printed #<HashMap {b=2, a=1}>
• link | changes

  ;; quick demonstration of using a Collections function on the resulting ArrayList
  
  user=> (def al (doto (java.util.ArrayList.) (.add 11) (.add 3)(.add 7)))
  #'user/al
  user=> al
  #<ArrayList [11, 3, 7]>
  user=> (java.util.Collections/sort al)
  nil
  user=> al
  #<ArrayList [3, 7, 11]>
  user=>

  ;; quick demonstration of using a Collections function on the resulting ArrayList user=> (def al (doto (java.util.ArrayList.) (.add 11) (.add 3)(.add 7))) #'user/al user=> al #<ArrayList [11, 3, 7]> user=> (java.util.Collections/sort al) nil user=> al #<ArrayList [3, 7, 11]> user=>
• link | changes

  ;; careful when calling 'dotimes' from within a 'doto' statement
  user=> (doto (java.util.ArrayList.)
               (.add -2)
               (.add -1)
               (dotimes [i 3] (.add i)))
  java.lang.IllegalArgumentException: dotimes requires a vector for its binding (NO_SOURCE_FILE:1)
  ; what has happened is that (java.util.ArrayList.) has secretly become the first argument to 'dotimes' and thus the exception informs us that it can't find the binding vector required for 'dotimes' to expand. You can cure this behaviour by simply using 'do' instead of 'doto' or by wrapping the call to 'dotimes' in a function. e.g:
  
  ;using 'let' with implicit 'do' instead of 'doto'
  user=> (let [al (java.util.ArrayList.)]
           (.add al -2)
           (.add al -1)
           (dotimes [i 3] (.add al i))
           al);return the ArrayList
  #<ArrayList [-2, -1, 0, 1, 2]>  ;exactly what we intended
  
  ;wrapping 'dotimes' in a function literal
  user=>(doto (java.util.ArrayList.)
              (.add -2)
              (.add -1)
              (#(dotimes [i 3] (.add % i))))
  #<ArrayList [-2, -1, 0, 1, 2]>  ;exactly what we intended again
  

  ;; careful when calling 'dotimes' from within a 'doto' statement user=> (doto (java.util.ArrayList.) (.add -2) (.add -1) (dotimes [i 3] (.add i))) java.lang.IllegalArgumentException: dotimes requires a vector for its binding (NO_SOURCE_FILE:1) ; what has happened is that (java.util.ArrayList.) has secretly become the first argument to 'dotimes' and thus the exception informs us that it can't find the binding vector required for 'dotimes' to expand. You can cure this behaviour by simply using 'do' instead of 'doto' or by wrapping the call to 'dotimes' in a function. e.g: ;using 'let' with implicit 'do' instead of 'doto' user=> (let [al (java.util.ArrayList.)] (.add al -2) (.add al -1) (dotimes [i 3] (.add al i)) al);return the ArrayList #<ArrayList [-2, -1, 0, 1, 2]> ;exactly what we intended ;wrapping 'dotimes' in a function literal user=>(doto (java.util.ArrayList.) (.add -2) (.add -1) (#(dotimes [i 3] (.add % i)))) #<ArrayList [-2, -1, 0, 1, 2]> ;exactly what we intended again