EmptyBox type

Represents absence of a value

Direct parent types

Box: A box which might (FullBox) or might not (EmptyBox) contain a value. Box is somewhat similar to Arr of zero (EmptyBox) or exactly one (FullBox) element. This analogy helps understanding each() and filter() operation.
Direct subtypes: 2

NoData: Absence of data
Direct subtypes: 2

Methods

Bool(eb:EmptyBox) Source: stdlib.ngs:2704: Always false

dflt(eb:EmptyBox, x:Any) Source: stdlib.ngs:2844

Wrap x in a Box

Returns

FullBox with the value x

Example

my_array = [10, 20]
# dflt on FullBox has no effect
my_array.Box(1).dflt(100).map(X*2).each(echo)
# output: 40
# dflt on EmptyBox creates FullBox with the given value
my_array.Box(5).dflt(100).map(X*2).each(echo) # HERE
# output: 200

each(eb:EmptyBox, cb:Fun) Source: stdlib.ngs:2728

Do nothing

Returns

Example

Box(null).each(echo)  # No output

filter(eb:EmptyBox, predicate:Any) Source: stdlib.ngs:2744

Do nothing

Returns

Example

EmptyBox().filter(X>20)  # <EmptyBox>

get(eb:EmptyBox) Source: stdlib.ngs:2772: Get EmptyBox value. Always throws BoxFail.

get(eb:EmptyBox, dflt:Any) Source: stdlib.ngs:2778: Get EmptyBox value
Returns
dflt

map(eb:EmptyBox, mapper:Fun) Source: stdlib.ngs:2718

Do nothing

Returns

Example

EmptyBox().map(X*2)  # <EmptyBox>