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shape_of

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A shape/type checker for Ruby objects.
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ShapeOf

A RubyGem that provides a way to verify "shapes" of objects.

This is licenced under the MIT license, Copyright 2022 John Isom.

Example Usage

Taken from lib/shape_of.rb.

For example, given this hash, where friendly_name, external_id, external_avatar_url, and data are optional:

hash = {
  id: 123,
  name: "John Doe",
  friendly_name: "Johnny",
  external_id: "",
  external_avatar_url: "https://example.com/avatar.jpg",
  data: {
    status: "VIP"
  },
  identities: [
    {
      id: 1,
      type: "email",
      identifier: "john37@example.com"
    }
  ],
  created_at: "2020-12-28T15:55:35.121Z",
  updated_at: "2020-12-28T15:55:35.121Z"
}

the proper shape would be this:

shape = ShapeOf::Hash[
  id: Integer,
  name: String,
  friendly_name: ShapeOf::Optional[String],
  external_id: ShapeOf::Optional[String],
  external_avatar_url: ShapeOf::Optional[String],
  data: ShapeOf::Optional[Hash],
  identities: ShapeOf::Array[
    ShapeOf::Hash[
      id: Integer,
      type: String,
      identifier: String
    ]
  ],
  created_at: String,
  updated_at: String
]

shape.shape_of? hash # => true

As another example, given this shape:

hash_shape = ShapeOf::Hash[
  value: ShapeOf::Optional[
    ShapeOf::Union[
      ShapeOf::Array[
        ShapeOf::Hash[
          inner_value: ShapeOf::Any
        ]
      ],
      ShapeOf::Hash[
        inner_value: ShapeOf::Any
      ]
    ]
  ]
]

These shapes pass:

hash_shape.shape_of?({ value: { inner_value: 3 } }) # => true
hash_shape.shape_of?({ value: [{ inner_value: 3 }] }) # => true
hash_shape.shape_of?({ value: [{ inner_value: 3 }, { inner_value: "foo" }, { inner_value: [1, 2, 3] }] }) # => true

And these fail:

hash_shape.shape_of?({ foo: { inner_value: 'bar' } }) # => false
hash_shape.shape_of?({ value: 23 }) # => false
hash_shape.shape_of?({ value: [23] }) # => false
hash_shape.shape_of?({ value: [{}] }) # => false

Other Usage

Alternatively, ShapeOf can be used with ruby objects rather than ShapeOf::Hash and ShapeOf::Array:

ShapeOf::Hash[
  id: Integer,
  identities: [
    {
      id: Integer,
      data: {
        type: String
      }
    }
  ]
]
# that is equivalent to:
ShapeOf::Hash[
  id: Integer,
  identities: ShapeOf::Array[
    ShapeOf::Hash[
      id: Integer,
      data: ShapeOf::Hash[
        type: String
      ]
    ]
  ]
]
# which in turn is equivalent to
{
  id: Integer,
  identities: [
    {
      id: Integer,
      data: {
        type: String
      }
    }
  ]
}.to_shape_of

ShapeOf can also be used to test actual values instead of classes. For example:

shape = ShapeOf::Union["hello", "world", "foobar", 1, 1.423]

shape.shape_of? "hello" # => true
shape.shape_of? "world" # => true
shape.shape_of? "foobar" # => true
shape.shape_of? 1 # => true
shape.shape_of? 1.423 # => true
shape.shape_of? "other string" # => false
shape.shape_of? nil # => false
shape.shape_of? 1.42300001 # => false
shape.shape_of? Object.new # => false

So, if you wanted to test that the field foo in a hash is optional but if it exists it either is a String or the integers 1-5, you could do so like this:

shape = ShapeOf::Hash[bar: String, foo: ShapeOf::Optional[ShapeOf::Union[String, *1..5]]]

shape.shape_of?({ bar: 'foobar' }) # => true
shape.shape_of?({}) # => false
shape.shape_of?({ bar: '', foo: 1 }) # => true
shape.shape_of?({ bar: '', foo: 2 }) # => true
shape.shape_of?({ bar: '', foo: 3 }) # => true
shape.shape_of?({ bar: '', foo: 4 }) # => true
shape.shape_of?({ bar: '', foo: 5 }) # => true
shape.shape_of?({ bar: '', foo: 6 }) # => false
shape.shape_of?({ bar: '', foo: "6" }) # => true
shape.shape_of?({ bar: '', foo: nil }) # => true

The Validator

New in v3.0.0, ShapeOf comes with a validator to make testing the shape of objects even easier. See this example usage:

a_shape = ShapeOf::Hash[foo: "bar", baz: Integer]
an_object = { foo: "bar", baz: 525 }

validator = ShapeOf::Validator.new(shape: a_shape, object: an_object)

validator.valid? # => true
validator.errors # => nil

And for a shape that doesn't match up:

a_shape = ShapeOf::Hash[
  non_existent: ShapeOf::Nothing,
  is_existent: String,
  list: ShapeOf::Array[Integer],
  union: ShapeOf::Union[0, 1, ShapeOf::Boolean, "true", "false", Class]
]
an_object = {
  non_existent: "should have error here",
  list: [1, "12", "234", 2, 5, nil],
  union: "yes" 
}

validator = ShapeOf::Validator.new(shape: a_shape, object: an_object)

validator.valid? # => false
validator.errors # => {"is_existent"=>{:errors=>["required key not present"]}, "non_existent"=>{:errors=>["key present when not allowed"]}, "list"=>{:idx_1=>{:errors=>["\"12\" is not instance of Integer"]}, :idx_2=>{:errors=>["\"234\" is not instance of Integer"]}, :idx_5=>{:errors=>["nil is not instance of Integer"]}}, "union"=>{:errors=>["\"yes\" is not shape of any of (ShapeOf::Boolean) or is not instance of any of (Class) or is not equal to (==) any of (0, 1, \"true\", \"false\")"]}}

Provided Shapes

ShapeOf::Hash

Pulled from comments from the source code:

Hash[key: shape, ...] denotes it is a hash of shapes with a very specific structure. Hash (without square brackets) is just a hash with any shape. This, along with Array, are the core components of this module. Note that the keys are converted to strings for comparison for both the shape and object provided.

Example:

# note that keyword args can be provided directly or wrapped in curly braces
shape = ShapeOf::Hash[foo: String, bar: ShapeOf::Hash[{ baz: Integer }]]

shape.shape_of?({ foo: "", bar: { baz: 1 } }) # => true
shape.shape_of?({ foo: "foo", bar: { baz: -2 } }) # => true
shape.shape_of?({}) # => false
shape.shape_of?({ bar: { baz: 2 } }) # => false
shape.shape_of?({ foo: "foo", bar: {} }) # => false
shape.shape_of?({ foo: "foo", bar: { baz: -2, blamo: nil } }) # => false
shape.shape_of?({ foo: "foo", bar: { baz: -2 }, blamo: nil }) # => false

ShapeOf::Array

Pulled from comments from the source code:

Array[shape] denotes that it is an array of shapes. It checks every element in the array and verifies that the element is in the correct shape. This, along with Hash, are the core components of this module. Note that a ShapeOf::Array[Integer].shape_of?([]) will pass because it is vacuously true for an empty array.

Example:

shape = ShapeOf::Array[String]

shape.shape_of?([]) # => true
shape.shape_of?(["foobar"]) # => true
shape.shape_of?(["a", "b", "c", "d"]) # => true
shape.shape_of?(["a", "b", 1, "d"]) # => false
shape.shape_of?(["a", "b", nil, "d"]) # => false

ShapeOf::Union

Pulled from comments from the source code:

Union[shape1, shape2, ...] denotes that it can be of one the provided shapes.

Example:

shape = ShapeOf::Union[String, ShapeOf::Array[String]]

shape.shape_of?("") # => true
shape.shape_of?("foo") # => true
shape.shape_of?([]) # => true
shape.shape_of?(["foo", "bar", "baz"]) # => true
shape.shape_of?(["foo", 1]) # => false
shape.shape_of?(nil) # => false

ShapeOf::Optional

Pulled from comments from the source code:

Optional[shape] denotes that the usual type is a shape, but is optional. (meaning if it is nil or the key is not present in the Hash, it's still true).

Example:

shape = ShapeOf::Optional[ShapeOf::Boolean]

shape.shape_of?(nil) # => true
shape.shape_of?(true) # => true
shape.shape_of?(false) # => true
shape.shape_of?(1) # => false
shape.shape_of?("") # => false

Example with ShapeOf::Hash:

shape = ShapeOf::Hash[foo: String, bar: ShapeOf::Optional[ShapeOf::Boolean]]

shape.shape_of?({ foo: "", bar: nil }) # => true
shape.shape_of?({ foo: "", bar: true }) # => true
shape.shape_of?({ foo: "", bar: false }) # => true
shape.shape_of?({ foo: "" }) # => true
shape.shape_of?({ foo: "", bar: 1 }) # => false
shape.shape_of?({ foo: "", bar: "" }) # => false

ShapeOf::Pattern

The ShapeOf::Pattern[/regexp pattern/] is used to match a Regexp against a String using Regexp#match?.

shape = ShapeOf::Pattern[/foobar$/i]

shape.shape_of?("foobar") # => true
shape.shape_of?("fOobAr\n") # => true
shape.shape_of?("\n\nfoobar\n") # => true
shape.shape_of?("foo\nbarfoo\nfoobar\nfo\nobar\n") # => true
shape.shape_of?("There once was a barfoo who foobared. Foobar") # => true
shape.shape_of?("foo\nbar\n") # => false

ShapeOf::Boolean

ShapeOf::Union[TrueClass, FalseClass]

ShapeOf::Numeric

ShapeOf::Union[Integer, Float, Rational, Complex]

ShapeOf::Any

Anything matches unless key does not exist in the ShapeOf::Hash.

ShapeOf::Nothing

Only passes when the key does not exist in the ShapeOf::Hash.

With MiniTest

Included is a ShapeOf::Assertions module which includes 2 methods: assert_shape_of, and refute_shape_of. Keep in mind that the order of the "expected" and "actual" value for these assertions are backwards of what Minitest assertions are.

In ShapeOf, by default, the actual comes first, then the expected shape comes after. However, with the release of v3.0.0, the correct order can be used, by calling ShapeOf::Assertions.use_proper_expected_actual_order! before using any of the assertions in your tests.

# test.rb
require 'shape_of'
ShapeOf::Assertions.use_proper_expected_actual_order!

require 'minitest/autorun'

class MyTestClass < MiniTest::Test
  include ShapeOf::Assertions

  def test_a_shape
    to_test = [{ foo: 1, bar: nil }, { foo: 34 }]
    assert_shape_of(ShapeOf::Array[
      ShapeOf::Hash[
        foo: Integer,
        bar: ShapeOf::Optional[Integer],
      ]
    ], to_test) # assertion passes

    assert_shape_of(ShapeOf::Array[
      ShapeOf::Hash[
        foo: "whoa",
        bar: "nil",
        baz: nil
      ]
    ], to_test) # assertion fails with this message:
=begin
 FAIL MyTestClass#test_a_shape (0.15s)
        {:idx_0=>
          {"baz"=>{:errors=>["required key not present"]},
           "foo"=>{:errors=>["1 is not equal to (==) \"whoa\""]},
           "bar"=>{:errors=>["nil is not equal to (==) \"nil\""]}},
         :idx_1=>
          {"bar"=>{:errors=>["required key not present"]},
           "baz"=>{:errors=>["required key not present"]},
           "foo"=>{:errors=>["34 is not equal to (==) \"whoa\""]}}}
=end
  end
end