flatten_as

Adds Enumerable#flatten_as that is like flatten with compile time control over what is flattened.

Installation

Add this to your application's shard.yml:

dependencies:
  flatten_as:
    github: jbomanson/flatten_as

Usage

This library adds the following method to Enumerable:

def flatten_as(target_type : U.class) : U forall U

Flattens self partially and converts the result into an enumerable of type U.

require "flatten_as"

# Flattening into a one dimensional array.
[2, [4, [1]], [[3]]].flatten_as(Array(Int32)) # => [2, 4, 1, 3]

# Flattening into a two dimensional array.
[[4, [1]], [[3]]].flatten_as(Array(Array(Int32))) # => [[4, 1], [3]]

# Flattening into a two dimensional set.
[[4, [1]], [[3]]].flatten_as(Set(Set(Int32))) # => Set{Set{4, 1}, Set{3}}

# Casting elements.
[2, 4, 1, 3].flatten_as(Array(Int32 | Float32)) # => [2, 4, 1, 3]

More specifically, this flattening works as follows.

Suppose self is a type similar to Array(Indexable(Set(Iterator(X)))). In general, it can be any type starting with some number of nested Enumerable types. The last type, X, can be anything other than a plain Enumerable type. In other words, it can be an Int32 or some union type for example, even if that union type includes an Enumerable.

The target type U must also an Enumerable. Suppose it is Set(Array(Y)). The important thing here is that all the Enumerable types that U begins with must be constructible with a new method that takes no arguments and must respond to a << method. The last type, Y, is again anything other than a plain Enumerable type.

In this setting, the flattening method will:

• cast the non Enumerable part X of self as Y

• flatten the Enumerable part of self that extends beyond U in depth, namely Set(Iterator(...))

• recreate the leading Enumerable part of self that is as deep as U as an instance of the target type, which in this case means to recreate Array(Indexable(...)) as Set(Array(Y)).

Contributing

1. Fork it ( https://github.com/jbomanson/flatten_as/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• jbomanson Jori Bomanson - creator, maintainer