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