optional

optional is a simple library that wraps over java.util.Optional and offers convenience methods for easy implementation in Clojure code.

How to use the library

All functions are available through the fr33m0nk.optional and fr33m0nk.utility namespaces. Add the following to your project dependencies:

• CLI/deps.edn dependency information:

net.clojars.fr33m0nk/optional {:mvn/version "0.1.7"}

• Leningen/Boot

[net.clojars.fr33m0nk/optional "0.1.7"]

• Maven:

<dependency>
    <groupId>net.clojars.fr33m0nk</groupId>
    <artifactId>optional</artifactId>
    <version>0.1.7</version>
</dependency>

Require at the REPL with:

(require 
  '[fr33m0nk.optional :as optional]
  '[fr33m0nk.utility :as optional-util])

Or in your namespace as:

(ns mynamespace
  (:require [fr33m0nk.optional :as optional]
    [fr33m0nk.utility :as optional-util]))

Functions and macros:

Name	Description
fr33m0nk.optional/optional-of	Returns Optional of supplied value
fr33m0nk.optional/wrap-fn	Wraps Clojure fn try catch block to return Optional values
fr33m0nk.optional/has-value?	Returns boolean based on whether Optional has value or is empty
fr33m0nk.optional/=	Like core/= for Optionals
fr33m0nk.optional/get	Retrieves the value boxed in Optional
fr33m0nk.optional/filter	Returns Optional value satisfying predicate
fr33m0nk.optional/map	Transforms value boxed in Optional by applying supplied mapping function and returns Optional<T>
fr33m0nk.optional/flat-map	Transforms value boxed in Optional by applying supplied mapping function that themselves returns Optional<T>. Un-nests Optional<Optional<T>> and returns Optional<T>
fr33m0nk.utility/fn->predicate	Takes a Clojure predicate function and returns a java.util.function.Predicate instance
fr33m0nk.utility/fn->function	Takes a Clojure function for mapping and returns a java.util.function.Function instance

API Docs

• Detailed usages of below functions can be found in tests
• Collections should not be wrapped in an optional as any collection by itself could represent the absence of data by being empty.
• If the control flow of code (or it's part) is driven by Exception (or it's subclasses), refrain from using Optionals or this library in them.
• Read this and this for right practices of using Optional.

• namespace

(ns fr33m0nk.optional)

optional-of

• Returns an Optional
• Zero arity version returns an empty Optional
• Single arity version returns an Optional of value
• If nil is supplied as value, returns an empty Optional

Usage:

(require '[fr33m0nk.optional :as optional])

(optional/optional-of 10)
;;=> #object[java.util.Optional 0x21bf3689 "Optional[10]"]

(optional/optional-of)
;;=> #object[java.util.Optional 0x1341289b "Optional.empty"]

wrap-fn

• Take a Clojure Fn f and returns a Clojure Fn that is wrapped in try catch block
• Returned fn when executed returns Optional of value if application was successful or empty Optional when execution of supplied function throws an Exception
• Multi arity versions also take a exception handler which can be a logger function
• If logger is a macro e.g. clojure.tools.logging, create a logger-fn and supply that as argument
• e.g.

(def logger-fn #(clojure.tools.logging/info % "Exception occurred"))

• The reason is Clojure functions can't take macros as argument

Usage:

(require '[fr33m0nk.optional :as optional]
         '[fr33m0nk.utility :as optional-util]
         '[clojure.tools.logging :as log])

(inc "10")
;;Execution error (ClassCastException) at user/eval1972 (form-init6918060955066684574.clj:1).
;;class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')

;; Example without logger
(let [wrapped-inc (optional/wrap-fn inc)]
  (wrapped-inc 1))
;;=> #object[java.util.Optional 0x57226b51 "Optional[2]"]

;; Example with logger
(let [log-fn #(clojure.tools.logging/info %)
      wrapped-inc (optional/wrap-fn inc log-fn)]
  (wrapped-inc "1"))
;; Aug 15, 2022 12:32:04 PM clojure.tools.logging$eval2267$fn__2270 invoke
;; INFO: {:msg class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap'), :type java.lang.ClassCastException, :exception {:via [{:type java.lang.ClassCastException, :message "class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')", :at [clojure.lang.Numbers inc "Numbers.java" 139]}], :trace [[clojure.lang.Numbers inc "Numbers.java" 139] [clojure.core$inc invokeStatic "core.clj" 929] [clojure.core$inc invoke "core.clj" 924] [clojure.lang.AFn applyToHelper "AFn.java" 154] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$apply invoke "core.clj" 662] [fr33m0nk.optional$warp_return_in_optional$fn__1959 doInvoke "optional.clj" 114] [clojure.lang.RestFn invoke "RestFn.java" 408] [user$eval2280 invokeStatic "form-init16753772140548043809.clj" 3] [user$eval2280 invoke "form-init16753772140548043809.clj" 1] [clojure.lang.Compiler eval "Compiler.java" 7194] [clojure.lang.Compiler eval "Compiler.java" 7149] [clojure.core$eval invokeStatic "core.clj" 3215] [clojure.core$eval invoke "core.clj" 3211] [nrepl.middleware.interruptible_eval$evaluate$fn__968$fn__969 invoke "interruptible_eval.clj" 87] [clojure.lang.AFn applyToHelper "AFn.java" 152] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$with_bindings_STAR_ invokeStatic "core.clj" 1990] [clojure.core$with_bindings_STAR_ doInvoke "core.clj" 1990] [clojure.lang.RestFn invoke "RestFn.java" 425] [nrepl.middleware.interruptible_eval$evaluate$fn__968 invoke "interruptible_eval.clj" 87] [clojure.main$repl$read_eval_print__9206$fn__9209 invoke "main.clj" 437] [clojure.main$repl$read_eval_print__9206 invoke "main.clj" 437] [clojure.main$repl$fn__9215 invoke "main.clj" 458] [clojure.main$repl invokeStatic "main.clj" 458] [clojure.main$repl doInvoke "main.clj" 368] [clojure.lang.RestFn invoke "RestFn.java" 1523] [nrepl.middleware.interruptible_eval$evaluate invokeStatic "interruptible_eval.clj" 84] [nrepl.middleware.interruptible_eval$evaluate invoke "interruptible_eval.clj" 56] [nrepl.middleware.interruptible_eval$interruptible_eval$fn__999$fn__1003 invoke "interruptible_eval.clj" 152] [clojure.lang.AFn run "AFn.java" 22] [nrepl.middleware.session$session_exec$main_loop__1067$fn__1071 invoke "session.clj" 202] [nrepl.middleware.session$session_exec$main_loop__1067 invoke "session.clj" 201] [clojure.lang.AFn run "AFn.java" 22] [java.lang.Thread run "Thread.java" 1534]], :cause class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')}}
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

has-value?

• Returns a boolean
• Checks if supplied Optional has a value or is empty

Usage:

(require '[fr33m0nk.optional :as optional])

(optional/has-value? (optional/optional-of 10))
;;=> true

(optional/has-value? (optional/optional-of))
;;=> false

=

• Returns a boolean
• Checks equality for Optionals

Usage:

(require '[fr33m0nk.optional :as optional])

(optional/= (optional/optional-of 10) (optional/optional-of 10) (optional/optional-of 10))
;;=> true

(optional/= (optional/optional-of 10) (optional/optional-of))
;;=> false

get

• Return nil for empty Optional
• Returns value contained in Optional
• Two arity version also takes another value that would be returned if Optional is empty

Usage:

(require '[fr33m0nk.optional :as optional])

(optional/get (optional/optional-of 10))
;;=> 10

(optional/get (optional/optional-of))
;;=> nil

filter

• Returns empty Optional if predicate evaluates to false or predicate throws Exception
• Returns Optional with value if predicate evaluates to true
• Multi arity versions also take a exception handler which can be a logger function
• If logger is a macro e.g. clojure.tools.logging, create a logger-fn and supply that as argument
• e.g.

(def logger-fn #(clojure.tools.logging/info % "Exception occurred"))

• The reason is Clojure functions can't take macros as argument

Usage:

(require '[fr33m0nk.optional :as optional]
         '[fr33m0nk.utility :as optional-util]
         '[clojure.tools.logging :as log])

(optional/filter (partial < 9) (optional/optional-of 10))
;;=> #object[java.util.Optional 0x21e87e90 "Optional[10]"]

(optional/filter (partial > 9) (optional/optional-of 10))
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

;; Example with logger and exception message
(let [log-fn #(clojure.tools.logging/info % "Uh-Oh!!")]
  (optional/filter (partial > 9) (optional/optional-of "10") log-fn))
;;Aug 15, 2022 12:48:14 PM clojure.tools.logging$eval2267$fn__2270 invoke
;;INFO: Uh-Oh!! {:msg class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap'), :type java.lang.ClassCastException, :exception {:via [{:type java.lang.ClassCastException, :message "class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')", :at [clojure.lang.Numbers gt "Numbers.java" 261]}], :trace [[clojure.lang.Numbers gt "Numbers.java" 261] [clojure.core$_GT_ invokeStatic "core.clj" 1079] [clojure.core$_GT_ invoke "core.clj" 1072] [clojure.core$partial$fn__5908 invoke "core.clj" 2641] [fr33m0nk.utility$fn$reify__1939 test "utility.clj" 42] [java.util.Optional filter "Optional.java" 218] [fr33m0nk.optional$filter invokeStatic "optional.clj" 59] [fr33m0nk.optional$filter invoke "optional.clj" 46] [user$eval2420 invokeStatic "form-init16753772140548043809.clj" 2] [user$eval2420 invoke "form-init16753772140548043809.clj" 1] [clojure.lang.Compiler eval "Compiler.java" 7194] [clojure.lang.Compiler eval "Compiler.java" 7149] [clojure.core$eval invokeStatic "core.clj" 3215] [clojure.core$eval invoke "core.clj" 3211] [nrepl.middleware.interruptible_eval$evaluate$fn__968$fn__969 invoke "interruptible_eval.clj" 87] [clojure.lang.AFn applyToHelper "AFn.java" 152] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$with_bindings_STAR_ invokeStatic "core.clj" 1990] [clojure.core$with_bindings_STAR_ doInvoke "core.clj" 1990] [clojure.lang.RestFn invoke "RestFn.java" 425] [nrepl.middleware.interruptible_eval$evaluate$fn__968 invoke "interruptible_eval.clj" 87] [clojure.main$repl$read_eval_print__9206$fn__9209 invoke "main.clj" 437] [clojure.main$repl$read_eval_print__9206 invoke "main.clj" 437] [clojure.main$repl$fn__9215 invoke "main.clj" 458] [clojure.main$repl invokeStatic "main.clj" 458] [clojure.main$repl doInvoke "main.clj" 368] [clojure.lang.RestFn invoke "RestFn.java" 1523] [nrepl.middleware.interruptible_eval$evaluate invokeStatic "interruptible_eval.clj" 84] [nrepl.middleware.interruptible_eval$evaluate invoke "interruptible_eval.clj" 56] [nrepl.middleware.interruptible_eval$interruptible_eval$fn__999$fn__1003 invoke "interruptible_eval.clj" 152] [clojure.lang.AFn run "AFn.java" 22] [nrepl.middleware.session$session_exec$main_loop__1067$fn__1071 invoke "session.clj" 202] [nrepl.middleware.session$session_exec$main_loop__1067 invoke "session.clj" 201] [clojure.lang.AFn run "AFn.java" 22] [java.lang.Thread run "Thread.java" 1534]], :cause class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')}}
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

map

• Returns empty Optional if f throws Exception
• Returns Optional with transformed value if f was applied successfully
• Multi arity versions also take a exception handler which can be a logger function
• If logger is a macro e.g. clojure.tools.logging, create a logger-fn and supply that as argument
• e.g.

(def logger-fn #(clojure.tools.logging/info % "Exception occurred"))

• The reason is Clojure functions can't take macros as argument

Usage:

(require '[fr33m0nk.optional :as optional]
         '[fr33m0nk.utility :as optional-util]
         '[clojure.tools.logging :as log])

(->> 9
     optional/optional-of
     (optional/map inc))
;;=> #object[java.util.Optional 0x6af3fba3 "Optional[10]"]

(->> "9"
     optional/optional-of
     (optional/map inc))
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

;; Example with logger and exception message
(let [log-fn #(clojure.tools.logging/info % "Uh-Oh!!")]
  (->> "9"
       optional/optional-of
       (#(optional/map inc % log-fn))))
;;Aug 15, 2022 12:51:46 PM clojure.tools.logging$eval2267$fn__2270 invoke
;;INFO: Uh-Oh!! {:msg class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap'), :type java.lang.ClassCastException, :exception {:via [{:type java.lang.ClassCastException, :message "class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')", :at [clojure.lang.Numbers inc "Numbers.java" 139]}], :trace [[clojure.lang.Numbers inc "Numbers.java" 139] [clojure.core$inc invokeStatic "core.clj" 929] [clojure.core$inc invoke "core.clj" 924] [fr33m0nk.utility$fn$reify__1942 apply "utility.clj" 61] [java.util.Optional map "Optional.java" 260] [fr33m0nk.optional$map invokeStatic "optional.clj" 73] [fr33m0nk.optional$map invoke "optional.clj" 61] [user$eval2442$fn__2445 invoke "form-init16753772140548043809.clj" 4] [user$eval2442 invokeStatic "form-init16753772140548043809.clj" 4] [user$eval2442 invoke "form-init16753772140548043809.clj" 1] [clojure.lang.Compiler eval "Compiler.java" 7194] [clojure.lang.Compiler eval "Compiler.java" 7149] [clojure.core$eval invokeStatic "core.clj" 3215] [clojure.core$eval invoke "core.clj" 3211] [nrepl.middleware.interruptible_eval$evaluate$fn__968$fn__969 invoke "interruptible_eval.clj" 87] [clojure.lang.AFn applyToHelper "AFn.java" 152] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$with_bindings_STAR_ invokeStatic "core.clj" 1990] [clojure.core$with_bindings_STAR_ doInvoke "core.clj" 1990] [clojure.lang.RestFn invoke "RestFn.java" 425] [nrepl.middleware.interruptible_eval$evaluate$fn__968 invoke "interruptible_eval.clj" 87] [clojure.main$repl$read_eval_print__9206$fn__9209 invoke "main.clj" 437] [clojure.main$repl$read_eval_print__9206 invoke "main.clj" 437] [clojure.main$repl$fn__9215 invoke "main.clj" 458] [clojure.main$repl invokeStatic "main.clj" 458] [clojure.main$repl doInvoke "main.clj" 368] [clojure.lang.RestFn invoke "RestFn.java" 1523] [nrepl.middleware.interruptible_eval$evaluate invokeStatic "interruptible_eval.clj" 84] [nrepl.middleware.interruptible_eval$evaluate invoke "interruptible_eval.clj" 56] [nrepl.middleware.interruptible_eval$interruptible_eval$fn__999$fn__1003 invoke "interruptible_eval.clj" 152] [clojure.lang.AFn run "AFn.java" 22] [nrepl.middleware.session$session_exec$main_loop__1067$fn__1071 invoke "session.clj" 202] [nrepl.middleware.session$session_exec$main_loop__1067 invoke "session.clj" 201] [clojure.lang.AFn run "AFn.java" 22] [java.lang.Thread run "Thread.java" 1534]], :cause class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')}}
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

flat-map

• Returns empty Optional if f throws Exception
• Returns Optional with transformed value if f transforms value
• Un-nests Optionals and returns a single Optional e.g. Optional<Optional<T>> -> Optional<T>
• This is useful when working with fn that return Optional values
• Multi arity versions also take a exception handler which can be a logger function
• If logger is a macro e.g. clojure.tools.logging, create a logger-fn and supply that as argument
• e.g.

(def logger-fn #(clojure.tools.logging/info % "Exception occurred"))

• The reason is Clojure functions can't take macros as argument

Usage:

(require '[fr33m0nk.optional :as optional]
         '[fr33m0nk.utility :as optional-util]
         '[clojure.tools.logging :as log])

;; optional/map returns Optional<Optional<T>> when the mapping fn return Optional<T>
(->> 9
     optional/optional-of
     (optional/map (optional/wrap-fn inc)))
;;=> #object[java.util.Optional 0x38629e44 "Optional[Optional[10]]"]

;; optional/flat-map returns Optional<T> even when the mapping fn return Optional<T>
(->> 9
     optional/optional-of
     (optional/flat-map (optional/wrap-fn inc)))
;;=> #object[java.util.Optional 0x244313a4 "Optional[10]"]

;; optional/map returns Optional<Optional<T>> when the mapping fn return Optional<T>
(->> "9"
     optional/optional-of
     (optional/map (optional/wrap-fn inc)))
;;=> #object[java.util.Optional 0x1278dd1b "Optional[Optional.empty]"]

;; optional/flat-map returns Optional<T> even when the mapping fn return Optional<T>
(->> "9"
     optional/optional-of
     (optional/flat-map (optional/wrap-fn inc)))
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

;; Example with logger and exception message when mapping function is returns unboxed value
(let [log-fn #(clojure.tools.logging/info % "Uh-Oh!!")]
  (->> "9"
       optional/optional-of
       (#(optional/flat-map inc % log-fn))))
;;Aug 15, 2022 12:59:06 PM clojure.tools.logging$eval2267$fn__2270 invoke
;;INFO: Uh-Oh!! {:msg class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap'), :type java.lang.ClassCastException, :exception {:via [{:type java.lang.ClassCastException, :message "class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')", :at [clojure.lang.Numbers inc "Numbers.java" 139]}], :trace [[clojure.lang.Numbers inc "Numbers.java" 139] [clojure.core$inc invokeStatic "core.clj" 929] [clojure.core$inc invoke "core.clj" 924] [fr33m0nk.utility$fn$reify__1942 apply "utility.clj" 61] [java.util.Optional flatMap "Optional.java" 289] [fr33m0nk.optional$flat_map invokeStatic "optional.clj" 89] [fr33m0nk.optional$flat_map invoke "optional.clj" 75] [user$eval2488$fn__2491 invoke "form-init16753772140548043809.clj" 4] [user$eval2488 invokeStatic "form-init16753772140548043809.clj" 4] [user$eval2488 invoke "form-init16753772140548043809.clj" 1] [clojure.lang.Compiler eval "Compiler.java" 7194] [clojure.lang.Compiler eval "Compiler.java" 7149] [clojure.core$eval invokeStatic "core.clj" 3215] [clojure.core$eval invoke "core.clj" 3211] [nrepl.middleware.interruptible_eval$evaluate$fn__968$fn__969 invoke "interruptible_eval.clj" 87] [clojure.lang.AFn applyToHelper "AFn.java" 152] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$with_bindings_STAR_ invokeStatic "core.clj" 1990] [clojure.core$with_bindings_STAR_ doInvoke "core.clj" 1990] [clojure.lang.RestFn invoke "RestFn.java" 425] [nrepl.middleware.interruptible_eval$evaluate$fn__968 invoke "interruptible_eval.clj" 87] [clojure.main$repl$read_eval_print__9206$fn__9209 invoke "main.clj" 437] [clojure.main$repl$read_eval_print__9206 invoke "main.clj" 437] [clojure.main$repl$fn__9215 invoke "main.clj" 458] [clojure.main$repl invokeStatic "main.clj" 458] [clojure.main$repl doInvoke "main.clj" 368] [clojure.lang.RestFn invoke "RestFn.java" 1523] [nrepl.middleware.interruptible_eval$evaluate invokeStatic "interruptible_eval.clj" 84] [nrepl.middleware.interruptible_eval$evaluate invoke "interruptible_eval.clj" 56] [nrepl.middleware.interruptible_eval$interruptible_eval$fn__999$fn__1003 invoke "interruptible_eval.clj" 152] [clojure.lang.AFn run "AFn.java" 22] [nrepl.middleware.session$session_exec$main_loop__1067$fn__1071 invoke "session.clj" 202] [nrepl.middleware.session$session_exec$main_loop__1067 invoke "session.clj" 201] [clojure.lang.AFn run "AFn.java" 22] [java.lang.Thread run "Thread.java" 1534]], :cause class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')}}
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

;; Example with logger and exception message when mapping function is returns Optional<T>
(let [log-fn #(clojure.tools.logging/info % "Uh-Oh!!")
      mapping-fn (optional/wrap-fn inc log-fn)]
  (->> "9"
       optional/optional-of
       (optional/flat-map mapping-fn)))
;;Aug 15, 2022 12:57:43 PM clojure.tools.logging$eval2267$fn__2270 invoke
;;INFO: Uh-Oh!! {:msg class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap'), :type java.lang.ClassCastException, :exception {:via [{:type java.lang.ClassCastException, :message "class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')", :at [clojure.lang.Numbers inc "Numbers.java" 139]}], :trace [[clojure.lang.Numbers inc "Numbers.java" 139] [clojure.core$inc invokeStatic "core.clj" 929] [clojure.core$inc invoke "core.clj" 924] [clojure.lang.AFn applyToHelper "AFn.java" 154] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$apply invoke "core.clj" 662] [fr33m0nk.optional$warp_return_in_optional$fn__1959 doInvoke "optional.clj" 114] [clojure.lang.RestFn invoke "RestFn.java" 408] [fr33m0nk.utility$fn$reify__1942 apply "utility.clj" 61] [java.util.Optional flatMap "Optional.java" 289] [fr33m0nk.optional$flat_map invokeStatic "optional.clj" 89] [fr33m0nk.optional$flat_map invoke "optional.clj" 75] [fr33m0nk.optional$flat_map invokeStatic "optional.clj" 84] [fr33m0nk.optional$flat_map invoke "optional.clj" 75] [user$eval2478 invokeStatic "form-init16753772140548043809.clj" 5] [user$eval2478 invoke "form-init16753772140548043809.clj" 1] [clojure.lang.Compiler eval "Compiler.java" 7194] [clojure.lang.Compiler eval "Compiler.java" 7149] [clojure.core$eval invokeStatic "core.clj" 3215] [clojure.core$eval invoke "core.clj" 3211] [nrepl.middleware.interruptible_eval$evaluate$fn__968$fn__969 invoke "interruptible_eval.clj" 87] [clojure.lang.AFn applyToHelper "AFn.java" 152] [clojure.lang.AFn applyTo "AFn.java" 144] [clojure.core$apply invokeStatic "core.clj" 667] [clojure.core$with_bindings_STAR_ invokeStatic "core.clj" 1990] [clojure.core$with_bindings_STAR_ doInvoke "core.clj" 1990] [clojure.lang.RestFn invoke "RestFn.java" 425] [nrepl.middleware.interruptible_eval$evaluate$fn__968 invoke "interruptible_eval.clj" 87] [clojure.main$repl$read_eval_print__9206$fn__9209 invoke "main.clj" 437] [clojure.main$repl$read_eval_print__9206 invoke "main.clj" 437] [clojure.main$repl$fn__9215 invoke "main.clj" 458] [clojure.main$repl invokeStatic "main.clj" 458] [clojure.main$repl doInvoke "main.clj" 368] [clojure.lang.RestFn invoke "RestFn.java" 1523] [nrepl.middleware.interruptible_eval$evaluate invokeStatic "interruptible_eval.clj" 84] [nrepl.middleware.interruptible_eval$evaluate invoke "interruptible_eval.clj" 56] [nrepl.middleware.interruptible_eval$interruptible_eval$fn__999$fn__1003 invoke "interruptible_eval.clj" 152] [clojure.lang.AFn run "AFn.java" 22] [nrepl.middleware.session$session_exec$main_loop__1067$fn__1071 invoke "session.clj" 202] [nrepl.middleware.session$session_exec$main_loop__1067 invoke "session.clj" 201] [clojure.lang.AFn run "AFn.java" 22] [java.lang.Thread run "Thread.java" 1534]], :cause class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap')}}
;;=> #object[java.util.Optional 0x200c7eac "Optional.empty"]

optional->sequence

• Returns Clojure sequence from Optional<T>

Usage:

(->> 10
     optional/optional-of
     (optional/map inc)
     (optional/optional->sequence))
;;=> (11)

• namespace

(ns fr33m0nk.utility)

fn->predicate

• Takes a clojure predicate fn and returns a java.util.function.Predicate instance which is used with optional/filter
• Multi arity versions also take a exception handler which can be a logger function
• If logger is a macro e.g. clojure.tools.logging, create a logger-fn and supply that as argument
• e.g.

(def logger-fn #(clojure.tools.logging/info % "Exception occurred"))

• The reason is Clojure functions can't take macros as argument

Usage:

(require 
  '[fr33m0nk.utility :as optional-util]
  '[clojure.tools.logging :as log])

(def log-fn #(clojure.tools.logging/info % "Uh-Oh!!"))

(optional-util/fn->predicate inc log-fn)
;;=> #object[fr33m0nk.utility$fn$reify__1939 0x72489d41 "fr33m0nk.utility$fn$reify__1939@72489d41"]

fn->function

• Takes a clojure fn for mapping and returns a java.util.function.Function instance which is used with option/map and option/flat-map
• Multi arity versions also take a exception handler which can be a logger function
• If logger is a macro e.g. clojure.tools.logging, create a logger-fn and supply that as argument
• e.g.

(def logger-fn #(clojure.tools.logging/info % "Exception occurred"))

• The reason is Clojure functions can't take macros as argument

Usage:

(require 
  '[fr33m0nk.utility :as optional-util]
  '[clojure.tools.logging :as log])

(def log-fn #(clojure.tools.logging/info % "Uh-Oh!!"))

;; For map operations
(optional-util/fn->function inc log-fn false)

;; For flat-map operations
(optional-util/fn->function inc log-fn true)
;;=> #object[fr33m0nk.utility$fn$reify__1942 0x37917038 "fr33m0nk.utility$fn$reify__1942@37917038"]

Why would you WANT this?

Look, this is a judgement-free zone, OK? We all have our reasons.

License

Copyright © 2022 fr33m0nk (Prashant Sinha)

Distributed under the BSD 3-Clause License