Class: Brine::Coercing::Coercer

Inherits:
Object
  • Object
show all
Defined in:
lib/brine/coercing.rb

Overview

Coerces the types of provided objects to support assertion evaluation.

Coercion is used to support handling richer data types in Brine without introducing noisy type information to the language. Transformation code can be used to convert input provided directly to a Brine step, however data extracted from JSON will by default be limited to the small amount of JSON supported data types. As normally the data extracted from JSON will only be directly present on one side of the assertion (most likely the left), the simpler JSON data types can be coerced to a richer type based on the right hand side.

A standard example (and one which is supported in this file) is date/time values. When testing an API that returns such values it is likely desirable to perform assertions with proper date/time semantics, and the coercer allows such assertions against a value retrieved out of a JSON structure.

The combination of transforming of ParameterType inputs and the Coercer can also effectively allow for user defined types to seemlessly exist within the Brine tests.

Implementation (Most of the non-implementation info should later be moved).

Internally the Coercer is a wrapper around a map of coercion functions where the keys are the pairs of classes for the operands and the values are the functions which accept a pair of instances (ostensibly) of the classes and return a pair of transformed values. The default coercion function returns the inputs unmodified (a nop), so any pair of classes which does not have a key will pass through unchanged.

Note that this relies solely on the hash lookup and does not attempt any kind of inheritance lookup or similar. The current thinking is that there should be few expected types and lineage could be covered through explicit keys so the simple, dumb approach is likely sufficient.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Coercer

Instantiate a new Coercer.

Initialize the standard map of coercion functions.



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# File 'lib/brine/coercing.rb', line 55

def initialize
  @map = Hash.new(->(lhs, rhs){[lhs, rhs]})
  @map[[String, Time]] = ->(lhs, rhs){[Time.parse(lhs), rhs]}
end

Instance Method Details

#coerce(first, second) ⇒ Array

Coerce the provided inputs as needed.

Looks up and invokes the associated coercion function.

Parameters:

  • first (Object) —

    Provide the first operand.

  • second (Object) —

    Provide the second operand.

Returns:

  • (Array) —

    Return the coerced [first, second] values.



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# File 'lib/brine/coercing.rb', line 69

def coerce(first, second)
  @map[[first.class, second.class]].call(first, second)
end