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README.org: add documentation for Either

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Paul Campbell 2018-07-16 19:31:18 +01:00
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commit 78f15df464
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@ -722,3 +722,86 @@
#+END_SRC
** Either
Allows handling a value that can be one of two types, a left value/type or a
right value/type.
When an =Either= is returned from a method it will contain either a left or a
right.
Where the =Either= is used to represent success/failure, the left case is, by
convention, used to indicate the error, and right the success. An alternative
is to use the =Result= which more clearly distinguishes success from failure.
=Either= is not a Monad.
*** Static Constructors
**** =static <L, R> Either<L, R> left(final L l)=
Create a new Either holding a left value.
#+BEGIN_SRC java
final Either<Integer, String> left = Either.left(getIntegerValue());
#+END_SRC
**** =static <L, R> Either<L, R> right(final R r)=
Create a new Either holding a right value.
#+BEGIN_SRC java
final Either<Integer, String> right = Either.right(getStringValue());
#+END_SRC
*** Instance Methods
**** =boolean isLeft()=
Checks if the Either holds a left value.
#+BEGIN_SRC java
final boolean leftIsLeft = Either.<Integer, String>left(getIntegerValue()).isLeft();
final boolean rightIsLeft = Either.<Integer, String>right(getStringValue()).isLeft();
#+END_SRC
**** =boolean isRight()=
Checks if the Either holds a right value.
#+BEGIN_SRC java
final boolean leftIsRight = Either.<Integer, String>left(getIntegerValue()).isRight();
final boolean rightIsRight = Either.<Integer, String>right(getStringValue()).isRight();
#+END_SRC
**** =void match(Consumer<L> onLeft, Consumer<R> onRight)=
Matches the Either, invoking the correct Consumer.
#+BEGIN_SRC java
Either.<Integer, String>left(getIntegerValue())
.match(
left -> handleIntegerValue(left),
right -> handleStringValue(right)
);
#+END_SRC
**** =<T> Either<T, R> mapLeft(Function<L, T> f)=
Map the function across the left value.
#+BEGIN_SRC java
final Either<Double, String> either = Either.<Integer, String>left(getIntegerValue())
.mapLeft(i -> i.doubleValue());
#+END_SRC
**** =<T> Either<L, T> mapRight(Function<R, T> f)=
Map the function across the right value.
#+BEGIN_SRC java
final Either<Integer, String> either = Either.<Integer, String>left(getIntegerValue())
.mapRight(s -> s + "x");
#+END_SRC