With name equivalence, two types are the same if they are declared using the same name e. With structural equivalence, two types are compatible if they have a compatible structure, i.
Structural compatibility becomes interesting when pointer types are involved; the pointed to types need to be checked and loops can occur, e. While most types are easily checked for structural compatibility, every now and again aggregate types connect together in a way that makes it non-trivial to figure out which types are structurally compatible dot file ; needs graphviz :.
Handling the edge cases requires maintaining a stack of information about which pairs of types are currently being compared. In C, type compatibility is a combination of name equivalence for aggregate types in the same translation unit and structural equivalence for function types and aggregate types across translation units. Function types have to use structural equivalence because the type in a function definition is anonymous the function name that appears in the definition has this anonymous type , there is no name to compare.
Cycles cannot appear in function types in C , because the identifier being defined in a typedef is not in scope until just after the completion of its declarator. It is not possible to refer to the identifier being defined insider its own definition e. Were the solution steps not detailed enough? Was the language and grammar an issue?
Didn't find yours? Ask a new question Get plagiarism-free solution within 48 hours. Review Please. Next Previous. Related Questions. What is the difference between name equivalence and structural equivalence for type checking? What are the advantages of each?
Be sure to use the four criteria in your discussion. A union, intersection or difference can only be performed between two relations if they are type compatible. What is meant by type compatibility? A type is comparable a. A type is bounded if there is a minimum value of the type and a maximum value of the type. A type is showable , or is a showtype if values of the type can be converted to strings.
A type is callable if values of its type can be called on, or applied to, other values. A type is monoidal , or is a monoid , if it has an associative composition operator, and an identity operator for the composition. We can arrange types by building them up algebraically, similar to how sets are built up, for example:.
Are types extra-lingual, or are they themselves values? If values, are they first-class? Also if values, do they themselves belong to one of possibly many types or is there just one type? If not, can they be categorized into different, um, say, typeclasses? What exactly are the types of the language, and how are new types built? How do we infer the type of an expression gets tricky with variables How do we know when two types are exactly the same? How do we know when two types are compatible?
What do we do when expressions are used in a way inconsistent with their type? Fixed Type Systems Some languages predefine the set of types and do not let you define new ones. Erlang : The only types are: atom, integer, float, binary, ref, pid, port, function, list, tuple, map. JavaScript really does have only eight types, but it kind of feels like it has more. Are Types Values? Types in JavaScript are extra-lingual.
So asking for the type of an expression might be an indication of a type system that is less sophisticated than it could be. In C, you can't even ask or check for a type, but you can see them! The types exist in the code, but they are not values that can be assigned to variables or passed as arguments or returned from functions. Exercise : Try writing C code that uses int as a value.
What problems do you run into? In Python, on the other hand, the value has the type int , and int itself is a value in Python. In fact it has the type type. And, you guessed it, type is a value whose type is Integer System. String System. Class Augh, wait, WTF Types vs. Classes So what is this thing we call a class? A little hard to define, maybe Some languages conflate the notion of type and class, but most people agree there is a difference. But only one class: String.
The exceptions to this rule are JavaScript and CoffeeScript, where the word class does not make a type: instead it is a funny way of declaring a function and a prototype. Go has struct s for the class-concept and interface s for the pure behavior-only types. Oversimplying just a bit A class is an object factory; a type is a behavioral specification.
Type Expressions In many languages, you get a set of basic types and mechanisms for making new types. SML has type called int list. Does Python? No, in Python, the type is just called list.
0コメント