Box type

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 parent types

Eachable1: Eachable which each() calls the callback with one argument
Direct subtypes: 17

Direct children types

EmptyBox: Represents absence of a value

FullBox: Represents presence of a value
Direct subtypes: 8

Constructors

Box(x:Any) Source: stdlib.ngs:4303

Convert anything to Box (always FullBox)

Parameters

x	value to enclose in a box

Returns

FullBox with given value

Example

Box(7).map(X*2).get()  # 14

Box() Source: stdlib.ngs:4310

Convert Box with no arg to EmptyBox

Returns

EmptyBox

Example

Box() == EmptyBox()
Box().get(10)  # 10
Box().map(X*2).get()  # InvalidArgument exception (in "get()")

Box(n:Null) Source: stdlib.ngs:4319

Convert null to Box (always EmptyBox)

Returns

EmptyBox

Example

Box(null) == EmptyBox()
Box(null).map(X*2).get()  # InvalidArgument exception (in "get()")

Box(a:Arr, idx:Int) Source: stdlib.ngs:4331

Convert array value indexed by the given index

Parameters

idx	key to look in hash

Returns

Box. FullBox if the array has the element indexed by idx, EmptyBox otherwise.

Example

my_array = [10, 20]
my_array.Box(1).map(X*2).each(echo)
# output: 40
my_array.Box(5).map(X*2).each(echo)
# no output

Box(h:Hash, k:Any) Source: stdlib.ngs:4342

Convert hash value indexed by the given key to a Box

Parameters

k	key to look in hash

Returns

Box. FullBox if the hash has the element referenced by k, EmptyBox otherwise.

Example

my_hash = {"a": 10, "b": 300}
my_hash.Box("a").map(X*2).each(echo)
# output: 20
my_hash.Box("nope").map(X*2).each(echo)
# no output

Box(s:Success) Source: stdlib.ngs:7456

Convert Success to FullBox

Returns

FullBox

Example

Box("abcd" ~ /^(..)/).map({"First two letters: ${A[1]}"}).get("(too short)")  # First two letters: ab

Box(f:Failure) Source: stdlib.ngs:7463

Convert failure to EmptyBox

Returns

EmptyBox

Example

Box("a" ~ /^(..)/).map({"First two letters: ${A[1]}"}).get("(too short)")  # (too short)

Methods

==(b1:Box, b2:Box) Source: stdlib.ngs:4378

Compare boxes. Empty boxes and boxes with same content are considered to be equal.

Returns

Bool

Example

EmptyBox() == EmptyBox()
EmptyBox() != FullBox(1)
FullBox(1) == FullBox(1)
FullBox(1) != FullBox(2)

del(t:TmpFsObj, kcp:KeepCleanupPolicy, e:Box) Source: stdlib.ngs:5890: Undocumented

del(t:TmpFsObj, rcp:RemoveCleanupPolicy, e:Box) Source: stdlib.ngs:5895: Undocumented

del(t:TmpFsObj, koecp:KeepOnErrorCleanupPolicy, e:Box) Source: stdlib.ngs:5905: Undocumented

ExitCode(b:Box) Source: stdlib.ngs:4224: Zero for FullBox and one for EmptyBox