Strict value is not null coalesced from a false value

[arepnikov]

Resolves #28 (Strict value can't be null coalesced from a false value)

Background

Ruby's conditional assignment operator (||=) is typically used for assigning default values to variables:

def some_method(some_variable=nil)
  some_variable ||= "some-default-value"
  # ...
end

However, it has an issue with boolean values:

def some_method(some_boolean_variable=nil)
  some_boolean_variable ||= true
  # ...
end

If false is passed to some_method, the conditional assignment operator will treat false exactly the same as nil. As a result, boolean variables must be given default values differently from other types of values:

def some_method(some_boolean_variable=nil)
  some_boolean_variable = true if some_boolean_variable.nil?
  # ...
end

Proposed Standard: Boolean Attributes With Default Value

Messaging Handle has an boolean attribute strict, which has a default value:

def strict
  @strict ||= Defaults.strict
end
attr_writer :strict

This is a mistake, since the conditional assignment operator can't be used with boolean value. Instead, we propose the following:

def strict
  @strict = Defaults.strict if @strict.nil?
  @strict
end
attr_writer :strict

This proposed standard follows the existing norm for how default boolean values are assigned to local variables in methods.

[ntl]

In subst-attr, there's an example of a different form of nil-coalescing for booleans:

def some_method(some_boolean=nil)
  if some_boolean.nil?
    some_boolean = Defaults.some_boolean
  end
  ...
end

Reference: https://github.com/eventide-project/subst-attr/blob/master/lib/subst_attr/substitute.rb#L6-L8

Casing also has yet another form:

def some_method(some_boolean=nil)
  some_boolean = some_boolean.nil? ? false : some_boolean
  ...
end

Reference: https://github.com/eventide-project/casing/blob/master/lib/casing/camel/hash.rb#L5

[ntl]

The strict parameter is under consideration for removal.