Makes Box
play better with Scala for
comprehensions.
Returns true
if this Box
contains no value (i.e., it is Empty
or
Failure
or ParamFailure
).
The only time when you should be using this method is if the value is guaranteed to be available based on a guard outside of the method.
The only time when you should be using this method is if the value is
guaranteed to be available based on a guard outside of the method. In these
cases, please provide that information in the justification String
.
For example, User.currentUser.openOrThrowException("This snippet is only
used on pages where the user is logged in")
. For tests, use ==
or
===
instead. See the class documentation for more information.
A valid justification for using this method should not be "I want my code to fail fast when I call it." Using exceptions in the core logic of your application should be strongly discouraged.
Justify why calling this method is okay and why it will not result in an exception being thrown. This serves both as mandatory documentation and as a very clear indication of what unexpected thing happened in the event you were wrong about the guard.
The contents of the Box
if it is Full
.
NullPointerException
If you attempt to call it on an EmptyBox
,
with a message that includes the provided justification
.
Alias for pass
.
Returns true if the value contained in this box is equal to the specified value.
Returns true if the value contained in this box is equal to the specified
value. This is the same thing that ==
does when it's handed a value that
isn't a Box
, but using this is recommended because it's clearer that the
behavior will be different than the usual expectation.
Transform an Empty
to a Failure
with the specified message.
Transform an Empty
to a Failure
with the specified message. Otherwise
returns the same box.
A Failure
with the message if this Box
is Empty
, this box
otherwise.
This means a Failure
will also remain unchanged; see ?~!
to
change these.
Chain the given msg
as a Failure
ahead of any failures this Box
may
represent.
Chain the given msg
as a Failure
ahead of any failures this Box
may
represent.
If this is an Empty
, this method behaves like ?~
. If it is a Failure
,
however, this method returns a new Failure
with the given msg
and with its
chain
set to this Failure
.
As with ?~
, if this is a Full
, we return it unchanged.
A Failure
with the message if this Box
is an Empty
box. Chain
this box to the new Failure
if this is a Failure
. The unchanged
box if it is a Full
.
Create a Full
box containing the specified value if this box's value is
of type B
and Empty
otherwise.
Create a Full
box containing the specified value if this box's value is
of type B
and Empty
otherwise.
For example:
scala> Full("boom").asA[Int] res0: net.liftweb.common.Box[Int] = Empty scala> Full(5).asA[Int] res1: net.liftweb.common.Box[Int] = Full(5)
Equivalent to flatMap(f1).or(alternative)
.
If the partial function is defined at the current Box's value, apply the partial function.
An alias for collect
.
An alias for collect
.
Although this function is different for true collections, because Box
is
really a collection of 1, the two functions are identical.
Alias for ?~!
.
Equivalent to map(f).openOr(dflt)
.
Returns an Iterator
over the value
contained in this Box
, if any.
For Full
and Empty
, this has the expected behavior.
For Full
and Empty
, this has the expected behavior. Equality in terms
of Failure checks for equivalence of failure causes:
Failure("boom") == Failure("boom") Failure("bam") != Failure("boom") Failure("boom", Full(someException), Empty) != Failure("boom")
For other values, determines equality based upon the contents of this Box
instead of the box itself. As a result, it is not symmetric. As an example:
val foo = "foo" val boxedFoo = Full(foo) foo == boxedFoo //is false boxedFoo == foo //is true
It is safest to use ===
explicitly when you're looking for this behavior,
and use ==
only for box-to-box comparisons:
Full("magic") == Full("magic") Full("magic") != Full("another") Full("magic") != Empty Full("magic") != Failure("something's gone wrong")
If this Box
contains a value and it satisfies the specified func
,
return true
.
If this Box
contains a value and it satisfies the specified func
,
return true
. Otherwise, return false
.
true
if this Box does contain a value and it satisfies the
predicate.
Alias for ?~
.
If this Box
contains a value and it satisfies the specified predicate
,
return the Box
unchanged.
If this Box
contains a value and it satisfies the specified predicate
,
return the Box
unchanged. Otherwise, return an Empty
.
If this Box
contains a value and it satisfies the specified predicate
,
return the Box
unchanged.
If this Box
contains a value and it satisfies the specified predicate
,
return the Box
unchanged. Otherwise, return a Failure
with the given
msg
.
A Failure
with the message if the box is empty or the predicate
is not satisfied by the value contained in this Box.
If this Box
contains a value and it does not satisfy the specified
f
, return the Box
unchanged.
If this Box
contains a value and it does not satisfy the specified
f
, return the Box
unchanged. Otherwise, return an Empty
.
Apply a function returning a Box
to the value contained in this Box
if
it exists and return the resulting Box
.
Apply a function returning a Box
to the value contained in this Box
if
it exists and return the resulting Box
. If this Box
is not already
Full
, return this box unchanged.
This means that using flatMap
with a Failure
will preserve the
Failure.
If this Box
contains a value and it does not satisfy the specified
func
, return false
.
If this Box
contains a value and it does not satisfy the specified
func
, return false
. Otherwise, return true
.
true If the Box
is empty, or if its value satisfies the
predicate.
Perform a side effect by calling the specified function with the value contained in this box.
Perform a side effect by calling the specified function with the value
contained in this box. The function does not run if this Box
is empty.
If the Box
is Full
, apply the transform function f
on the value v
;
otherwise, just return the value untransformed.
If the Box
is Full
, apply the transform function f
on the value v
;
otherwise, just return the value untransformed.
The transform function is expected to be a function that will take the
value v
and produce a function from the value in the box to a new value
of the same type as v
.
For example:
val myBox = Full(10) myBox.fullXForm("No teddy bears left.")({ message => { teddyBears: Int => s"$message Oh wait, there are $teddyBears left!" } })
The type of the initial value, default value, and transformed value.
If the Box
is Full
, the value once transformed by the function
returned by f
. Otherwise, the initial value v
.
Exists to avoid the implicit conversion from Box
to Option
.
Exists to avoid the implicit conversion from Box
to Option
. Opening a
Box
unsafely should be done using openOrThrowException
.
This method always throws an exception.
If this box is Full
and contains an object of type B
, returns a Full
of type Box[B]
.
If this box is Full
and contains an object of type B
, returns a Full
of type Box[B]
. Otherwise, returns Empty
.
This is basically a Java-friendly version of asA
, which you should
prefer when using Scala.
For example:
scala> Full("boom").isA(classOf[Int]) res0: net.liftweb.common.Box[Int] = Empty scala> Full(5).isA(classOf[Int]) res1: net.liftweb.common.Box[Int] = Full(5)
Returns true if the box contains a value.
Returns an Iterator
over the value
contained in this Box
, if any.
Get a java.util.Iterator
from the Box.
Apply a function to the value contained in this Box
if it exists and return
a Full
containing the result.
Apply a function to the value contained in this Box
if it exists and return
a Full
containing the result. If this Box
is not already Full
, return
the unchanged box.
This means that using map
with a Failure
will preserve the
Failure.
Return the value contained in this Box
if it is full; otherwise return
the specified default.
Return the value contained in this Box
if it is full; otherwise return
the specified default. Equivalent to Option
's getOrElse
.
Return this Box if Full
, or the specified alternative if it is
empty.
Return this Box if Full
, or the specified alternative if it is
empty. Equivalent to Option
's orElse
.
Perform a side effect by passing this Box
to the specified function and
return this Box
unmodified.
Perform a side effect by passing this Box
to the specified function and
return this Box
unmodified. Similar to foreach
, except that foreach
returns Unit
, while this method allows chained use of the Box
.
This box.
This method calls the specified function with the specified in
value and
the value contained in this Box
.
This method calls the specified function with the specified in
value and
the value contained in this Box
. If this box is empty, returns the in
value directly.
The result of the function or the in
value.
An Either
that is a Right
with the given argument
right
if this is empty, or a Left
with the boxed value if this is
Full
.
Returns a List
of one element if this
is Full, or an empty list if empty.
Returns the contents of this box wrapped in Some
if this is Full
, or
None
if this is empty (meaning an Empty
, Failure
or ParamFailure).
An Either
that is a Left
with the given argument
left
if this is empty, or a Right
with the boxed value if this is
Full
.
Makes Box
play better with Scala for
comprehensions.
Transform an Empty
or Failure
to a ParamFailure
with the specified
type-safe parameter.
Transform an Empty
or Failure
to a ParamFailure
with the specified
type-safe parameter.
A value indicating the error.
A ParamFailure
with the specified value, unless this is already a
ParamFailure
or a Full
. If this is a Failure
, the
ParamFailure
will preserve the message of the Failure
.
The
Box
class is a container which is able to declare if it isFull
(containing a single non-null value) orEmptyBox
. AnEmptyBox
, or empty, can be theEmpty
singleton,Failure
orParamFailure
.Failure
andParamFailure
contain information about why theBox
is empty including exception information, possibly chainedFailure
s and aString
message.This serves a similar purpose to the
Option
class from Scala standard library but adds several features:Failure
object if it isEmpty
(with the?~
orfailMsg
method).Failure
s (with the?~!
orcompoundFailMsg
method).Box
, with a default to return if the box isEmpty
:Box
to a function for side effects:Exceptions and Empty Box Handling
If you grew up on Java, you're used to
Exception
s as part of your program logic. The Scala philosophy and the Lift philosophy is that exceptions are for exceptional conditions such as failure of an external resource (e.g., your database goes offline) rather than simply indicating that a parameter wasn't supplied or couldn't be parsed.Lift's
Box
and Scala'sOption
provide mechanisms for being explicit about a value existing or not existing rather than relying on a reference being not-null. However, extracting a value from aBox
should be done correctly. Available options are:for
comprehension, especially for multiple boxes:map
,flatMap
,filter
, andforeach
(for
comprehensions use these under the covers):Failure
s):==
and===
: