README.md
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# Taipo
Taipo is a simple library for checking the types of variables.
[Full documentation][rd] is available at RubyDoc.
[rd]: http://www.rubydoc.info/gems/taipo/index
## Overview
When we deal with variables in our code, we have certain expectations about what those variables can and can't do.
Taipo provides a simple way to make those expectations explicit. If an expectation isn't met, Taipo can either raise an exception or return the problematic variables for us to handle.
## Installation
Run `gem install taipo` or add `gem 'taipo'` to your `Gemfile`.
## Usage
Taipo can be used to check variables within a given context or check the return value of a given method:
* the `Taipo::Check` module provides two methods: `#check` and `#review`:
* the `Taipo::Result` module provides one method: `.result`.
### #check
```ruby
require 'taipo'
class Foo
include Taipo::Check
def double(val)
check types, val: 'Integer'
val * 2
end
end
foo = Foo.new
foo.double 5 #=> 10
foo.double 'Oops' #=> Taipo::TypeError
```
The method `#check` will raise an exception as soon as one of its arguments doesn't match its type definition.
[More information about `#check`][rdc] is available in the documentation.
[rdc]: http://www.rubydoc.info/gems/taipo/Taipo/Check#check-instance_method
### #review
```ruby
require 'taipo'
class Foo
include Taipo::Check
def add(x, y)
errors = review types, x: 'Integer', y: 'Integer'
if errors.empty?
x + y
else
'Oops'
end
end
end
foo = Foo.new
foo.add 4, 5 #=> 9
foo.add 2, 'OK' #=> 'Oops'
```
The method `#review` will put the invalid arguments into an array and return that to the user. If there are no errors, the array is empty.
[More information about `#review`][rdr] is available in the documentation.
[rdr]: http://www.rubydoc.info/gems/taipo/Taipo/Check#review-instance_method
### .result
```ruby
require 'taipo'
class Foo
include Taipo::Result
result :add, 'Integer'
def add(x, y)
x + y
end
end
foo = Foo.new
foo.add 4, 5 #=> 9
foo.add 'hello', 'world' #=> Taipo::TypeError
```
The method `.result` will raise an exception if the return value of the specified method doesn't match the specified type definition.
[More information about `.result`][rde] is available in the documentation.
[rde]: http://www.rubydoc.info/gems/taipo/Taipo/Result/ClassMethods#result-instance_method
## Syntax
Type definitions are written as Strings. Type definitions can consist of (1) names, (2) collections, (3) constraints and (4) sums.
The information in this README is only meant as an introduction. [More information about the type definition syntax][rdv] is available in the documentation.
[rdv]: http://www.rubydoc.info/gems/taipo/Taipo/Parser/Validater
### Names
The simplest case is to write the name of a class. For example, `'String'`. Inherited class names can also be used.
```ruby
check types, a: 'String', b: 'Numeric', c: 'Foo::Bar'
```
#### Duck Types
It's possible to specify a duck type by writing the instance method (or methods) to which the object should respond.
```ruby
check types, a: '#to_s', b: '(#foo, #bar)'
```
#### Optional Types
If `nil` is permitted as a value, the optional shorthand `?` can be appended to the end of a class name to form an optional type. Collections and constraints can follow as usual.
```ruby
check types, a: 'String?', b: 'Array?<Integer>', c: 'Integer?(min: 0)'
```
### Collections
Taipo can also check whether a variable has a collection of elements of the specified child type. A child type can consist of the same components as any other type (ie. a name, collection, constraint, sum).
```ruby
check types, a: 'Array<Integer>', b: 'Hash<Symbol, String>', c: 'Array<Array<Float>>'
```
### Constraints
Constraints can be added to a type definition. Constraints consist of a list of one or more identifier-value pairs. Instance method names can also be in included.
```ruby
check types, a: 'Array(len: 5)', b: 'Integer(min: 0, max: 10)', c: 'String(format: /a{3}/)', d: 'String(val: "Hello world!")', e: 'Foo(#bar)'
```
### Sums
Type definitions can be combined to form sum types. Sum types consist of two or more type definitions.
```ruby
check types, a: 'String|Float', b: 'Boolean|Array<String|Hash<Symbol,Point>|Array<String>>', c: 'Integer(max: 100)|Float(max: 100)'
```
#### Enums
It's possible to approximate an enum by writing a sum type consisting of Symbols.
```ruby
check types, a: ':foo|:bar', b: ':one|:two|:three'
```
## Requirements
Taipo has been tested with Ruby version 2.4.2.
## Bugs
Found a bug? I'd love to know about it. The best way is to report them in the [Issues section][ghi] on GitHub.
[ghi]: https://github.com/pyrmont/taipo/issues
## Contributing
If you're interested in contributing to Taipo, feel free to fork and submit a pull request.
## Versioning
Taipo uses [Semantic Versioning 2.0.0][sv2].
[sv2]: http://semver.org/
## Colophon
Taipo began as, and remains primarily, an exercise to improve my programming skills. If Taipo has piqued your interest in adding type checks to Ruby, consider some of the other options, such as [Contracts][cnt], [Rtype][rty], [Rubype][rub] or [Sig][sig].
[cnt]: https://github.com/egonSchiele/contracts.ruby
[rty]: https://github.com/sputnikgugja/rtype
[rub]: https://github.com/gogotanaka/Rubype
[sig]: https://github.com/janlelis/sig
## Licence
Taipo is released into the public domain. See [LICENSE.md][lc] for more details.
[lc]: https://github.com/pyrmont/taipo/blob/master/LICENSE.md