must.cr

Library for dynamic typing in Crystal.

Core class pollution

• Object#must

Features

• Checking Types : Dynamically guarantee object types
• Casting Types : Dynamically cast object types
• Matching Features : Object matching and data extraction

# checking
1.must(Int32) # => 1
1.must(Bool)  # raises Must::TypeError

# casting
1.must.cast(String) # => "1"
1.must.cast(Bool)   # raises Must::CastError

# matching
708.must.match(/0/)          # => 708
708.must.match(/0(.)/, "$1") # => "8"

• crystal: 0.31.1

Why not use as for casting?

• as checks types at compile time
• must checks type at runtime

json = JSON.parse(%|{"a": 1}|)
json["a"].as_f                   # Unhandled exception: cast from Int64 to Float64 failed (runtime)
json["a"].raw.to_f               # undefined method 'to_f' for Array(JSON::Any) (compile time)
json["a"].raw.must.cast(Float64) # => 1.0

Installation

1. Add the dependency to your shard.yml:

dependencies:
  must:
    github: maiha/must
    version: 0.2.0

2. Run shards install

Usage

require "must"

API

any?, any

Checks empty? or not. It returns true if the class doesn't have empty? method.

1.must.any?              # => true
1.must.any               # => 1
Set(Int32).new.any?      # => false
"".must.any?             # => false
"".must.any              # raises Must::Error("(value) is empty")
"".must.any(name: "foo") # raises Must::Error("foo is empty")

Development

Contributing

1. Fork it (https://github.com/maiha/must.cr/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

• maiha - creator and maintainer