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: 16

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:2786

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(n:Null) Source: stdlib.ngs:2791

Convert null to Box (always EmptyBox)

Returns

EmptyBox

Example

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

Box(a:Arr, idx:Any) Source: stdlib.ngs:2802

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:2820

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(my:MatchY) Source: stdlib.ngs:5274

Convert successful match to FullBox

Returns

FullBox

Example

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

Box(mn:MatchN) Source: stdlib.ngs:5279

Convert failed match 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:2856

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)

any(b:Box, predicate:Any) Source: stdlib.ngs:2750

Test Box value

Example

Box(5).any(Int)      # true
Box(5).any(Str)      # false
EmptyBox().any(Int)  # false

ExitCode(b:Box) Source: stdlib.ngs:2707: Zero for FullBox and one for EmptyBox

none(b:Box, predicate:Any) Source: stdlib.ngs:2760

Test Box value

Example

Box(5).none(Int)      # false
Box(5).none(Str)      # true
EmptyBox().none(Int)  # true