conditional/README.org

* Conditional

* Functional Condition and Value.

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* Maven

 #+BEGIN_SRC xml
 <dependency>
     <groupId>net.kemitix</groupId>
     <artifactId>conditional</artifactId>
     <version>RELEASE</version>
 </dependency>
 #+END_SRC

 The latest version should be shown above with the nexus and maven-central
 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]].


* Condition

  The `if ... then` and `if ... then ... else` constructs can't be used in a
  lambda without being wrapped in a code block.

  Using `Condition` allows the use of an if-style expression without needing to
  wrap it in a code block


** if-then

   #+BEGIN_SRC java
   if (isTrue()) {
       doSomething();
   }

   Condition.where(isTrue())
            .then(() -> doSomething());
   #+END_SRC


** if-then-else

   #+BEGIN_SRC java
   if (isTrue()) {
       doSomething();
   } else {
       doSomethingElse();
   }

   Condition.where(isTrue())
            .then(() -> doSomething())
            .otherwise(() -> doSomethingElse());
   #+END_SRC


** isTrue() / isFalse() / not()

   #+BEGIN_SRC java
   final Condition condition = Condition.where(isTrue());
   final boolean isTrue = condition.isTrue();
   final boolean isFalse = condition.isFalse();
   final Condition not = condition.not();
   final Condition andCondition1 = condition.and(Condition.where(isAlsoTrue()));
   final Condition andCondition2 = condition.and(isAlsoTrue());
   final Condition orCondition1 = condition.or(Condition.where(isAlsoTrue()));
   final Condition orCondition2 = condition.or(isAlsoTrue());
   #+END_SRC


** flatMap(Function<Boolean, Condition>)

   #+BEGIN_SRC java
   final Condition condition = Condition.where(isTrue())
                                        .flatMap(b -> Condition.where(b));
   #+END_SRC


** if-and-then-else

   #+BEGIN_SRC java
   if (isTrue() && isAlsoTrue()) {
       doSomething();
   } else {
       doSomethingElse();
   }

   Condition.where(isTrue())
            .and(() -> isAlsoTrue())
            .then(() -> doSomething())
            .otherwise(() -> doSomethingElse());
   #+END_SRC


** if-or-then-else

   #+BEGIN_SRC java
   if (isTrue() || alternativeIsTrue()) {
       doSomething();
   } else {
       doSomethingElse();
   }

   Condition.where(isTrue())
            .or(() -> alternativeIsTrue())
            .then(() -> doSomething())
            .otherwise(() -> doSomethingElse());
   #+END_SRC


** if-then-else-if

   #+BEGIN_SRC java
   if (isFalse()) {
       doSomething();
   } else if (isTrue()) {
       doSomethingElse();
   }

   Condition.where(isFalse())
            .then(() -> doSomething())
            .otherwise(() -> isTrue())
            .then(() -> doSomethingElse());
   #+END_SRC


** if-then-if-then

   #+BEGIN_SRC java
   if (isTrue()) {
       doSomething();
       if (isAlsoTrue()) {
           doSomethingElse();
       }
   }

   Condition.where(isTrue())
            .then(() -> doSomething())
            .and(() -> isAlsoTrue())
            .then(() -> doSomethingElse());
   #+END_SRC


* Value

  Values from an if-then-else in a functional-style.

  Functional, and verbose, alternative to the ternary operator (=?:=).


** if-then-else

   #+BEGIN_SRC java
   String result;
   if (isTrue()) {
       result = TRUE;
   } else {
       result = FALSE;
   }

   String result = isTrue() ? TRUE : FALSE;

   final String result = Value.where(isTrue(), () -> TRUE, () -> FALSE);

   final String result = Value.where(Condition.where(isTrue), () -> TRUE, () -> FALSE);

   final Optional<String> result = Value.where(isTrue(), () -> TRUE);

   final String result = Value.<String>where(isTrue())
                              .not()
                              .then(() -> FALSE)
                              .otherwise(() -> TRUE);
   #+END_SRC


** if-and-then-else

   #+BEGIN_SRC java
   String result;
   if (isTrue() && alternativeIsTrue()) {
       result = TRUE;
   } else {
       result = FALSE;
   }

   final String result = Value.<String>where(isTrue())
                              .and(() -> alternativeIsTrue())
                              .then(() -> TRUE)
                              .otherwise(() -> FALSE);
   #+END_SRC


** if-or-then-else

   #+BEGIN_SRC java
   String result;
   if (isTrue() || alternativeIsTrue()) {
       result = TRUE;
   } else {
       result = FALSE;
   }

   final String result = Value.<String>where(isTrue())
                              .or(() -> alternativeIsTrue())
                              .then(() -> TRUE)
                              .otherwise(() -> FALSE);
   #+END_SRC


** if-or-not-then-else

   #+BEGIN_SRC java
   String result;
   if (isTrue() || !isFalse()) {
   result = TRUE;
   } else {
   result = FALSE;
   }

   final String result = Value.<String>where(isTrue())
                              .orNot(() -> isFalse())
                              .then(() -> TRUE)
                              .otherwise(() -> FALSE);
   #+END_SRC


** if-then

   #+BEGIN_SRC java
   Optional<String> result;
   if (isTrue()) {
       result = Optional.of(TRUE);
   } else {
       result = Optional.empty();
   }

   final Optional<String> result = Value.<String>where(isTrue())
                                        .then(() -> TRUE)
                                        .optional();
   #+END_SRC