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Specifying Sub-Types

This doc will give you a quick overview of what some of the most important typical types are and what their sub-types mean

Dict​

Dict denotes the set of all dictionaries.
Two ways of specifying sub-types are possible:

Key-Value type specification​
D1 = Dict[String, Int]   # all keys are strings and vals are ints  
  
{'x': 42, 'y': 1} in D1        # True  
{'x': 42, 'y': 'one'} in D1    # False
Listing Key-Value Pairs​
D2 = Dict['x': Int, 'name': String]  
{'x': 42, 'name': 'Bob'} in D2     # True  
{'x': 42, 'name': 'Bob', 'one_more': 1} in D2     # False
  • The above notation "seals" the allowed key-value pairs. The required fields are listed.
  • the key is specified by value (the same in the type definition as in the value)
  • the value is specified by type
Openness to Extension​
D2 = Dict[  
            'x': Int,   
            'name': String,  
            ...                 # allow more key-val fields  
        ]  
  
{'x': 42, 'name': 'Bob', 'one_more': 1} in D2     # False

if you want to only list the required fields and not care if additional ones are present

Lists​

Lists in Zef are a higher level syntactic construct than in Python: they do not refer to the concrete low level representation of a value, but rather indicate "a sequence of items". 

[2, 'hello', True] | is_a[List]      # True  
(5, 6, 7) | is_a[List]               # True

Subtyping a list List[T1] can be done specifying any type T1: the resulting set denotes the set of all lists where every element in the list is of type (contained in the set) T1: 

[3, 4, 5] in List[Int]    # True  
[3, 'hi'] in List[Int]    # False

Specifying a subtype for a list does not say anything about the length of the lists.

Tuples​

Tuples (aka product types) are similar to Lists, but each specified subtype is applied to the element at the respective position: 

T3 = Tuple[Int, Float, String]  
[2, 4.5, 'hi'] in T3     # True  
[2, 4, 'hi'] in T3       # False: second element mismatch  
[2, 4.5] in T3           # False: length mismatch
Openness to Extension​

Similar to Dicts subtyping: ellipsis can be used 

T4 = Tuple[Int, String, ...]  # allow additional elements  
[4, 'hi'] in T4               # True  
[4, 'hi', 1.1, 1.2] in T4     # True  
[4] in T4           # False: string required as second element