An enumerable which is guaranteed to have at least one element. E.g., #first
will never fail.
These four methods give non-empty-aware access:
#first#last
#tail#all_but_last
And one method for mutating the list:
#push
Sometimes I know that an Array isn't empty. Or more accurately, it shouldn't be empty, because otherwise, it means there's a bug in my code. The usual way to handle this is to repeatedly check the array's length, or check for nil, and throw an exception if, for some reason, the Array is empty. We've all been there.
The NonEmptyArray approach saves this work by moving the non-emptyness
into the type system, letting Ruby check and prevent misuse. I.e., this class is
designed so that it's impossible for it to be empty. It has made illegal states unrepresentable.
And it has accessors like #first and #last which always return an element - they can never fail.
While Ruby isn't statically typed, the interpreter does check arity (the number of arguments provided).
So we enlist the interpreter's help to ensure a NonEmptyArray is always created with at least one
element:
require 'non_empty_array'
a = NonEmptyArray.new() # => Ruby error - missing parameterrequire 'non_empty_array'
a = NonEmptyArray.new('1000') # Simplest way to create one
a.count() # => 1
a.first() # => '1000'
a.push('2000')
a.count() # => 2require 'non_empty_array'
a = NonEmptyArray.new(100, [200, 300]). # Can also create from a head and tail
# Methods from Enumerable
a.count() # => 3
a.max() # => 300
a.to_a() # => [100, 200, 300]
# Methods specific to NonEmptyArray
a.first() # => 100 Always succeeds - never returns a "no element" error.
a.last() # => 300 Always succeeds
a.all_but_last() # => [100, 200] A normal array, which may indeed be empty.
a.push('400')
a.all_but_last() # => [100, 200, 300]
a.tail() # => [200, 300, 400]Inspired by Haskell's NonEmpty List.