Issues of Arrays In Programming Languages

Are Arrays first class?

• If the language has values, can an array be a value ?
• Can they be passed as parameters ?
• Can they be returned from functions ?
• Can you have an array of arrays ?

Array dimensions

Are the dimensions part of the type? Can you ...?

• Write polymorphic code ?
• Use an expression for the size ?
• Access the dimensions at run-time ?

Multi-dimensional Arrays

Questions:

• Is an array of arrays the same as a multi-dimensional array ?
• Is there supporting syntax ?
• Can you access a slice of an array ? (both rows and columns? portions of an array?)

Array typing

Questions:

• Can we have different array types ?
• Is there subtyping between them ?
• Can we write polymorphic code ?

Implementing arrays as references (e.g. Java)

Decisions:

• length specified at creation;
• length stored in array;
• no multi-dim arrays;
• slices hard to implement.

Implementing arrays as values (e.g. Ada)

Decisions:

• length part of type (optionally);
• polymorphic code over different lengths;
• multi-dim arrays;
• slices more possible.

Issues Of Records in Programming Languages 1

Are records first class?

• If the language has values, can a record be a value ?
• Can they be passed as parameters ?
• Can they be returned from functions ?
• Can you have a record of records ?

Issues Of Records in Programming Languages 2

What are the type rules?

• Does the type depend on the field names?
• Does the type depend on the order of field names?
• Is there width subtyping?
  (can fields be omitted in a supertype?)
• Is there depth subtyping?
  (can the subtype have a subtype for a field?)

Pointers, Mutation and Records

Can records be mutable?

• Is a record ``really'' a pointer?
• Do we need to put references into the record?
• Can records get new fields? How?

Field location

How do we locate fields?

• Are fields aligned?
• If so, what about the ``empty'' space? Does it get carried along? Does it affect equality comparison?
• Are fields ordered differently from their lexical order?

Variants, Tags, and Classes

• How do we distinguish the variants?
• Can a record change its variant?
• Can an object change its class?