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https://github.com/fr33m0nk/optional

A Clojure library that wraps over java.util.Optional
https://github.com/fr33m0nk/optional

clojure interop java optional

Last synced: about 1 month ago
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A Clojure library that wraps over java.util.Optional

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README 

          
## optional [![Clojars Project](https://img.shields.io/clojars/v/net.clojars.fr33m0nk/optional.svg)](https://clojars.org/net.clojars.fr33m0nk/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:

```clojure

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

```

- Leningen/Boot

```clojure

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

```

- Maven:

```xml



    net.clojars.fr33m0nk

    optional

    0.1.7



```

Require at the REPL with:



```clojure

(require 

  '[fr33m0nk.optional :as optional]

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

```



Or in your namespace as:



```clojure

(ns mynamespace

  (:require [fr33m0nk.optional :as optional]

    [fr33m0nk.utility :as optional-util]))

```



## Functions and macros:



| Name                                                          | Description                                                                                                                                                                    |

|---------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|

| [`fr33m0nk.optional/optional-of`](#optional-of)               | Returns Optional of supplied value                                                                                                                                             |

| [`fr33m0nk.optional/wrap-fn`](#wrap-fn)                       | Wraps Clojure fn `try catch` block to return Optional values                                                                                                                   |

| [`fr33m0nk.optional/has-value?`](#has-value?)                 | Returns boolean based on whether Optional has value or is empty                                                                                                                |

| [`fr33m0nk.optional/=`](#=)                                   | Like `core/=` for Optionals                                                                                                                                                    |

| [`fr33m0nk.optional/get`](#get)                               | Retrieves the value boxed in Optional                                                                                                                                          |

| [`fr33m0nk.optional/filter`](#filter)                         | Returns Optional value satisfying predicate                                                                                                                                    |

| [`fr33m0nk.optional/map`](#map)                               | Transforms value boxed in Optional by applying supplied mapping function and returns `Optional`                                                                             |

| [`fr33m0nk.optional/flat-map`](#flat-map)                     | Transforms value boxed in Optional by applying supplied mapping function that themselves returns `Optional`.
Un-nests `Optional>` and returns `Optional` |

| [`fr33m0nk.utility/fn->predicate`](#fn->predicate)            | Takes a Clojure predicate function and returns a `java.util.function.Predicate` instance                                                                                       |

| [`fr33m0nk.utility/fn->function`](#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](https://github.com/fr33m0nk/optional/blob/master/test/fr33m0nk/optional_test.clj)

- **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](https://stackoverflow.com/questions/26327957/should-java-8-getters-return-optional-type/26328555#26328555) and [this](https://stackoverflow.com/a/73097167/19613290) for right practices of using Optional.

- ### namespace

```clojure 

(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:

```clojure

(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.

```clojure

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

```

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

#### Usage:

```clojure

(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:

```clojure

(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:

```clojure

(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:

```clojure

(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.

```clojure

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

```

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

#### Usage:

```clojure

(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.

```clojure

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

```

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

#### Usage:

```clojure

(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`

- 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.

```clojure

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

```

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

#### Usage:

```clojure

(require '[fr33m0nk.optional :as optional]

         '[fr33m0nk.utility :as optional-util]

         '[clojure.tools.logging :as log])



;; optional/map returns Optional> when the mapping fn return Optional

(->> 9

     optional/optional-of

     (optional/map (optional/wrap-fn inc)))

;;=> #object[java.util.Optional 0x38629e44 "Optional[Optional[10]]"]



;; optional/flat-map returns Optional even when the mapping fn return Optional

(->> 9

     optional/optional-of

     (optional/flat-map (optional/wrap-fn inc)))

;;=> #object[java.util.Optional 0x244313a4 "Optional[10]"]



;; optional/map returns Optional> when the mapping fn return Optional

(->> "9"

     optional/optional-of

     (optional/map (optional/wrap-fn inc)))

;;=> #object[java.util.Optional 0x1278dd1b "Optional[Optional.empty]"]



;; optional/flat-map returns Optional even when the mapping fn return Optional

(->> "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

(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`

#### Usage:

```clojure

(->> 10

     optional/optional-of

     (optional/map inc)

     (optional/optional->sequence))

;;=> (11)

```

- ### namespace

```clojure 

(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.

```clojure

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

```

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

#### Usage:

```clojure

(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.

```clojure

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

```

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

#### Usage:

```clojure

(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