Class: ReSorcery::Decoder

Inherits:
Object
  • Object
show all
Includes:
Helpers
Defined in:
lib/re_sorcery/decoder.rb,
lib/re_sorcery/decoder/builtin_decoders.rb

Overview

Test that an object satisfies some property

A Decoder represents a piece of logic for verifying some property. A simple example would be a Decoder that verifies that an object is_a?(String). A ReSorcery::Result is used to represent the result of the logic. This can be created like:

is_string =
  Decoder.new { |n| n.is_a?(String) ? ok(n) : err("Expected String, got #{n.class}") }

And then used like:

is_string.test("I'm a string") #=> ok("I'm a string")
is_string.test(:symbol) #=> err("Expected String, got Symbol")

Because returning the original object wrapped in ok is the common result when a Decoder passes, a shorthand in the initializer is to return true, and Decoder will wrap the object for you.

is_string =
  Decoder.new { |n| n.is_a?(String) || err("Expected String, got #{n.class}") }

A similar shorthand: Since the alternative is always something wrapped in err, if anything but true or a Result is returned, it will be wrapped in err.

is_string =
  Decoder.new { |n| n.is_a?(String) || "Expected String, got #{n.class}" }

All three of these implementations of is_string are equivalent.

Note that this library has strong opinions against using nil, so nil will never pass Decoder#test.

Defined Under Namespace

Modules: BuiltinDecoders

Instance Method Summary collapse

Constructor Details

#initialize(&block) ⇒ Decoder

Returns a new instance of Decoder.



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# File 'lib/re_sorcery/decoder.rb', line 43

def initialize(&block)
  @block = block
  freeze
end

Instance Method Details

#and ⇒ Object

Chain decoders and maintain any transformed value

pos = is(String, Symbol)
  .map(&:to_sym)
  .and { |s, u| [:a, :b, :c].include?(s) || "Invalid option: #{u.inspect}" }

pos.test(:a) == ok(:a)
pos.test("a") == ok(:a)
pos.test("d") == err('Invalid option: "d"')


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# File 'lib/re_sorcery/decoder.rb', line 111

def and
  and_then do |value|
    Decoder.new do |unknown|
      Decoder.new { yield(value, unknown) }.test(value)
    end
  end
end

#and_then(decoder = nil, &block) ⇒ Object

Chain decoders

The second decoder can be chosen based on the (successful) result of the first decoder.

Note: the second decoder decodes the "original" unknown value, not the potentially-changed result of the first decoder.

Decoder.new { |u| u.is_a?(Symbol) || "Not symbol" }
  .map(&:to_s)
  .and_then { |v| Decoder.new { |u| true } } # v is a String & u is a Symbol
  .test(:a_symbol)

The block must return a Decoder.



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# File 'lib/re_sorcery/decoder.rb', line 90

def and_then(decoder = nil, &block)
  ArgCheck['decoder', decoder, Decoder] unless decoder.nil?

  Decoder.new do |unknown|
    test(unknown).and_then do |value|
      # Don't try to re-assign `decoder` here, because it's captured from outside the Decoder
      (decoder || ArgCheck['block.call(value)', block.call(value), Decoder]).test(unknown)
    end
  end
end

#assign(key, other) ⇒ Object

Chain decoders like and_then, but use the chain to build an object



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# File 'lib/re_sorcery/decoder.rb', line 133

def assign(key, other)
  ArgCheck['key', key, Symbol]
  ArgCheck['other', other, Proc, Decoder]
  other = ->(_) { other.call } if other.is_a?(Proc) && other.arity.zero?

  and_then do |a|
    ArgCheck['decoded value', a, Hash]

    decoder = other.is_a?(Decoder) ? other : ArgCheck['other.call', other.call(a), Decoder]
    decoder.map { |b| a.merge(key => b) }
  end
end

#map(&block) ⇒ Object

Apply some block within the context of a successful decoder



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# File 'lib/re_sorcery/decoder.rb', line 67

def map(&block)
  Decoder.new { |unknown| test(unknown).map(&block) }
end

#map_error(&block) ⇒ Object

Apply some block within the context of an unsuccessful decoder



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# File 'lib/re_sorcery/decoder.rb', line 72

def map_error(&block)
  Decoder.new { |unknown| test(unknown).map_error(&block) }
end

#or_else(decoder = nil, &block) ⇒ Object

If the Decoder failed, try another Decoder

The block must return a Decoder.



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# File 'lib/re_sorcery/decoder.rb', line 122

def or_else(decoder = nil, &block)
  ArgCheck['decoder', decoder, Decoder] unless decoder.nil?

  Decoder.new do |unknown|
    test(unknown).or_else do |value|
      (decoder || ArgCheck['block.call(value)', block.call(value), Decoder]).test(unknown)
    end
  end
end

#test(unknown) ⇒ Result

Use the decoder to test that an unknown object satisfies some property

Note that ok(nil) will never be returned.

Parameters:

  • unknown (unknown)

Returns:



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# File 'lib/re_sorcery/decoder.rb', line 54

def test(unknown)
  block_result = @block.call(unknown)
  case block_result
  when Result::Ok, Result::Err
    block_result
  when TrueClass
    ok(unknown)
  else
    err(block_result)
  end
end