Utility Classes :: IsAllOf

Overview

The IsAllOf class is used to specify that the object must meet all of any number of criterion, e.g., be an instance of certain types or user-defined classes, or be validated by other extension classes [1].

The IsAllOf() constructor must be passed at least two ([2]) distinct ([3]) types, user-defined classes or registered extension classes. For example:

@accepts(int, int, IsAllOf(Red, Green))
def my_func(a, b, c):
    pass

The following code snippet matches the signature:

class Christmas_tree(Red, Green):
	pass

oh_tannenbaum = Christmas_tree()

my_func(3, 3, oh_tannenbaum)

The requirement that there are two distinct conditions stems from the fact that the following call is almost certainly an error:

IsAllOf(Red, Red)

Details

• If the object being checked by the IsAllOf instance does not match all of the provided conditions, a _TC_TypeError will be raised; the right attribute will be the IsAllOf instance, and the wrong attribute will be the type of the object. [4]

  This exception is to be caught and converted to a TypeCheckError before it reaches the level of the user.

• IsAllOf objects will only compare equal (i.e., ==) if all the conditions in the left-hand side are found in the right-hand side, and vice versa [5].

  All IsAllOf instances that compare equal with == will produce the same value when run through the built-in hash() function [6].

• The IsAllOf class has been given some intelligence about boolean equality, meaning that it will optimise the creation of certain instances. For instance:

  IsAllOf(IsAllOf(A, B), IsAllOf(C, D))

  is equivalent to

  IsAllOf(A, B, C, D)

  In fact, the first will be coerced into the second, meaning that the two will compare and hash as equals [5, 6].

• Another coercion-related intelligence is this:

  IsAllOf(int, int, float, float)

  will be simplified to

  IsAllOf(int, float)

  Again, these two will compare and hash as equals [5, 6]. To expand on the boolean-equality example:

  IsAllOf(IsAllOf(A, B), IsAllOf(B, C))

  is equivalent to

  IsAllOf(A, B, C)

• The order in which the IsNoneOf instance's conditions will be checked is undefined.

References

1. test_utility_classes.py: Test_And.test_success
2. test_utility_classes.py: Test_And.test_constructor
3. test_utility_classes.py: Test_And.test_distinct_parameters
4. test_utility_classes.py: Test_And.test_failure
5. test_utility_classes.py: Test_And.test_equality
6. test_utility_classes.py: Test_And.test_hash