README.org: adjust headings
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318
README.org
318
README.org
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@ -39,150 +39,146 @@
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The latest version should be shown above with the nexus and maven-central
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badges or can be found on [[https://search.maven.org/#search%7Cga%7C1%7Cg%3A%22net.kemitix%22%20AND%20a%3A%22mon%22][Maven Central]].
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** Usage
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** TypeAlias
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:PROPERTIES:
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:CUSTOM_ID: usage
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:CUSTOM_ID: typealias
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:END:
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*** TypeAlias
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:PROPERTIES:
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:CUSTOM_ID: typealias
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:END:
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In Haskell it is possible to create an alias for a Type, and to then use
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that alias with the same behaviour as the original, except that the compiler
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doesn't treat the alias as the same Type and will generate compiler errors
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if you try and use them together. e.g.:
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In Haskell it is possible to create an alias for a Type, and to then use
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that alias with the same behaviour as the original, except that the compiler
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doesn't treat the alias as the same Type and will generate compiler errors
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if you try and use them together. e.g.:
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#+BEGIN_SRC haskell
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type PhoneNumber = String
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type Name = String
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type PhoneBook = [(Name,PhoneNumber)]
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#+END_SRC
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#+BEGIN_SRC haskell
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type PhoneNumber = String
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type Name = String
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type PhoneBook = [(Name,PhoneNumber)]
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#+END_SRC
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In Java we don't have the ability to have that true alias, so TypeAlias is
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more of a type-wrapper. It's as close as I could get to a Haskell type alias
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in Java.
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In Java we don't have the ability to have that true alias, so TypeAlias is
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more of a type-wrapper. It's as close as I could get to a Haskell type alias
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in Java.
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The benefits of using TypeAlias are:
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The benefits of using TypeAlias are:
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- encapsulation of the wrapped type when passing references through code
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that doesn't need to access the actual value, but only to pass it on
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- type-safe parameters where you would otherwise be passing Strings,
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Integers, Lists, or other general classes
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- equality and hashcode
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- less verbose than implementing your own
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- encapsulation of the wrapped type when passing references through code
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that doesn't need to access the actual value, but only to pass it on
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- type-safe parameters where you would otherwise be passing Strings,
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Integers, Lists, or other general classes
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- equality and hashcode
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- less verbose than implementing your own
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*TypeAlias Example:*
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*TypeAlias Example:*
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#+BEGIN_SRC java
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class PhoneNumber extends TypeAlias<String> {
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private PhoneNumber(final String value) {
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super(value);
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}
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public static PhoneNumber of(final String phoneNumber) {
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return new PhoneNumber(phoneNumber);
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}
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}
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#+END_SRC
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#+BEGIN_SRC java
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class PhoneNumber extends TypeAlias<String> {
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private PhoneNumber(final String value) {
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super(value);
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}
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public static PhoneNumber of(final String phoneNumber) {
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return new PhoneNumber(phoneNumber);
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}
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}
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#+END_SRC
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*Roll your own:*
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*Roll your own:*
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#+BEGIN_SRC java
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class PhoneNumber {
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private final String value;
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private PhoneNumber(final String value) {
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this.value = value;
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}
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public static PhoneNumber of(final String phoneNumber) {
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return new PhoneNumber(phoneNumber);
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (o == null || getClass() != o.getClass()) return false;
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PhoneNumber that = (PhoneNumber) o;
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return Objects.equals(value, that.value);
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}
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@Override
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public int hashCode() {
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return Objects.hash(value);
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}
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public String getValue() {
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return value;
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}
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}
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#+END_SRC
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#+BEGIN_SRC java
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class PhoneNumber {
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private final String value;
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private PhoneNumber(final String value) {
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this.value = value;
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}
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public static PhoneNumber of(final String phoneNumber) {
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return new PhoneNumber(phoneNumber);
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (o == null || getClass() != o.getClass()) return false;
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PhoneNumber that = (PhoneNumber) o;
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return Objects.equals(value, that.value);
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}
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@Override
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public int hashCode() {
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return Objects.hash(value);
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}
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public String getValue() {
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return value;
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}
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}
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#+END_SRC
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*Lombok:*
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*Lombok:*
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Although, if you are using Lombok, that can be equally terse, both it and
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TypeAlias<String> coming in at 8 lines each, compared to 24 for rolling your
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own:
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Although, if you are using Lombok, that can be equally terse, both it and
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TypeAlias<String> coming in at 8 lines each, compared to 24 for rolling your
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own:
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#+BEGIN_SRC java
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@Value
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@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
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class PhoneNumber {
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private final String value;
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public static PhoneNumber of(final String phoneNumber) {
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return new PhoneNumber(phoneNumber);
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}
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}
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#+END_SRC
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#+BEGIN_SRC java
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@Value
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@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
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class PhoneNumber {
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private final String value;
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public static PhoneNumber of(final String phoneNumber) {
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return new PhoneNumber(phoneNumber);
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}
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}
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#+END_SRC
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** Maybe
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:PROPERTIES:
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:CUSTOM_ID: maybe
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:END:
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*** Maybe
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:PROPERTIES:
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:CUSTOM_ID: maybe
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:END:
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Allows specifying that a value may or may not be present. Similar to
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=Optional=. =Maybe= provides additional methods that =Optional= doesn't:
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=isNothing()=, =stream()=, =ifNothing()= and =match()=. =Maybe= does not
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have a =get()= method.
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Allows specifying that a value may or may not be present. Similar to
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=Optional=. =Maybe= provides additional methods that =Optional= doesn't:
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=isNothing()=, =stream()=, =ifNothing()= and =match()=. =Maybe= does not
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have a =get()= method.
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Unlike =Optional=, when a =map()= results in a =null=, the =Maybe= will
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continue to be a =Just=. =Optional= would switch to being empty. [[http://blog.vavr.io/the-agonizing-death-of-an-astronaut/][vavi.io
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follows the same behaviour as =Maybe=]].
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Unlike =Optional=, when a =map()= results in a =null=, the =Maybe= will
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continue to be a =Just=. =Optional= would switch to being empty. [[http://blog.vavr.io/the-agonizing-death-of-an-astronaut/][vavi.io
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follows the same behaviour as =Maybe=]].
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#+BEGIN_SRC java
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import net.kemitix.mon.maybe.Maybe;
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#+BEGIN_SRC java
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import net.kemitix.mon.maybe.Maybe;
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import java.util.function.Function;
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import java.util.function.Predicate;
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import java.util.function.Function;
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import java.util.function.Predicate;
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class MaybeExample {
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class MaybeExample {
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public static void main(String[] args) {
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Maybe.just(countArgs(args))
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.filter(isEven())
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.map(validMessage())
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.match(
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just -> System.out.println(just),
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() -> System.out.println("Not an valid value")
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);
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}
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public static void main(String[] args) {
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Maybe.just(countArgs(args))
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.filter(isEven())
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.map(validMessage())
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.match(
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just -> System.out.println(just),
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() -> System.out.println("Not an valid value")
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);
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}
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private static Function<Integer, String> validMessage() {
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return v -> String.format("Value %d is even", v);
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}
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private static Function<Integer, String> validMessage() {
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return v -> String.format("Value %d is even", v);
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}
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private static Predicate<Integer> isEven() {
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return v -> v % 2 == 0;
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}
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private static Predicate<Integer> isEven() {
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return v -> v % 2 == 0;
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}
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private static Integer countArgs(String[] args) {
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return args.length;
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}
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}
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#+END_SRC
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private static Integer countArgs(String[] args) {
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return args.length;
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}
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}
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#+END_SRC
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In the above example, the number of command line arguments are counted, if
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there are an even number of them then a message is created and printed by
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the Consumer parameter in the =match= call. If there is an odd number of
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arguments, then the filter will return =Maybe.nothing()=, meaning that the
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=nothing= drops straight through the map and triggers the Runnable parameter
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in the =match= call.
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In the above example, the number of command line arguments are counted, if
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there are an even number of them then a message is created and printed by
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the Consumer parameter in the =match= call. If there is an odd number of
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arguments, then the filter will return =Maybe.nothing()=, meaning that the
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=nothing= drops straight through the map and triggers the Runnable parameter
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in the =match= call.
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**** =Maybe= is a Monad:
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@ -392,60 +388,60 @@
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.toOptional();
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#+END_SRC
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*** Result
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:PROPERTIES:
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:CUSTOM_ID: result
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:END:
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** Result
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:PROPERTIES:
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:CUSTOM_ID: result
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:END:
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Allows handling error conditions without the need to catch exceptions.
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Allows handling error conditions without the need to catch exceptions.
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When a =Result= is returned from a method it will contain one of two values.
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Either the actual result, or an error in the form of an =Exception=. The
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exception is returned within the =Result= and is not thrown.
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When a =Result= is returned from a method it will contain one of two values.
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Either the actual result, or an error in the form of an =Exception=. The
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exception is returned within the =Result= and is not thrown.
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#+BEGIN_SRC java
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import net.kemitix.mon.result.Result;
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#+BEGIN_SRC java
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import net.kemitix.mon.result.Result;
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import java.io.IOException;
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import java.io.IOException;
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class ResultExample implements Runnable {
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class ResultExample implements Runnable {
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public static void main(final String[] args) {
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new ResultExample().run();
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}
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public static void main(final String[] args) {
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new ResultExample().run();
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}
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@Override
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public void run() {
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Result.of(() -> callRiskyMethod())
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.flatMap(state -> doSomething(state))
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.match(
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success -> System.out.println(success),
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error -> error.printStackTrace()
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);
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}
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@Override
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public void run() {
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Result.of(() -> callRiskyMethod())
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.flatMap(state -> doSomething(state))
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.match(
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success -> System.out.println(success),
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error -> error.printStackTrace()
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);
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}
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private String callRiskyMethod() throws IOException {
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return "I'm fine";
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}
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private String callRiskyMethod() throws IOException {
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return "I'm fine";
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}
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private Result<String> doSomething(final String state) {
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return Result.of(() -> state + ", it's all good.");
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}
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private Result<String> doSomething(final String state) {
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return Result.of(() -> state + ", it's all good.");
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}
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}
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#+END_SRC
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}
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#+END_SRC
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In the above example the string ="I'm fine"= is returned by
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=callRiskyMethod()= within a successful =Result=. The =.flatMap()= call,
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unwraps that =Result= and, as it is a success, passes the contents to
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=doSomething()=, which in turn returns a =Result= that the =.flatMap()= call
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returns. =match()= is called on the =Result= and, being a success, will call
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the success =Consumer=.
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In the above example the string ="I'm fine"= is returned by
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=callRiskyMethod()= within a successful =Result=. The =.flatMap()= call,
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unwraps that =Result= and, as it is a success, passes the contents to
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=doSomething()=, which in turn returns a =Result= that the =.flatMap()= call
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returns. =match()= is called on the =Result= and, being a success, will call
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the success =Consumer=.
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Had =callRiskyMethod()= thrown an exception it would have been caught by the
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=Result.of()= method which would have then been an error =Result=. An error
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Result would have ignored the =flatMap= and skipped to the =match()= when it
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would have called the error =Consumer=.
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Had =callRiskyMethod()= thrown an exception it would have been caught by the
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=Result.of()= method which would have then been an error =Result=. An error
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Result would have ignored the =flatMap= and skipped to the =match()= when it
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would have called the error =Consumer=.
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**** =Result= is a Monad
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