Contents

---
title: Maybe
layout: gem-single
name: dry-types
---

The [dry-monads gem](/gems/dry-monads/) provides approach to handling optional values by returning a [_Monad_](/gems/dry-monads/) object. This allows you to pass your type to a `Maybe(x)` block that only executes if `x` returns `Some` or `None`.

> NOTE: Requires the [dry-monads gem](/gems/dry-monads/) to be loaded.
1. Load the `:maybe` extension in your application.

```ruby
require 'dry-types'

Dry::Types.load_extensions(:maybe)
module Types
  include Dry.Types()
end
```

2. Append `.maybe` to a _Type_ to return a _Monad_ object  

```ruby
x = Types::Maybe::Strict::Integer[nil]
Maybe(x) { puts(x) }
x = Types::Maybe::Coercible::String[nil]
Maybe(x) { puts(x) }
x = Types::Maybe::Strict::Integer[123]
Maybe(x) { puts(x) }
x = Types::Maybe::Strict::String[123]
Maybe(x) { puts(x) }
```

```ruby
Types::Maybe::Strict::Integer[nil] # None
Types::Maybe::Strict::Integer[123] # Some(123)
Types::Maybe::Coercible::Float[nil] # None
Types::Maybe::Coercible::Float['12.3'] # Some(12.3)
# 'Maybe' types can also accessed by calling '.maybe' on a regular type:
Types::Strict::Integer.maybe # equivalent to Types::Maybe::Strict::Integer
```

You can define your own optional types:

``` ruby
maybe_string = Types::Strict::String.maybe
maybe_string[nil]
# => None
maybe_string[nil].fmap(&:upcase)
# => None
maybe_string['something']
# => Some('something')
maybe_string['something'].fmap(&:upcase)
# => Some('SOMETHING')
maybe_string['something'].fmap(&:upcase).value_or('NOTHING')
# => "SOMETHING"
```

Version data entries

2 entries across 2 versions & 1 rubygems

Version	Path
dry-types-1.2.2	docsite/source/extensions/maybe.html.md
dry-types-1.2.1	docsite/source/extensions/maybe.html.md