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Comparison of Oberon-2 with Modula-2

This is a short summary of the main features offered by the programming language Oberon-2. The target audience is the Modula-2 programmer unfamiliar with Oberon-2, but familiar with object-oriented and extensible programming concepts.

Compared with its predecessor Modula-2, Oberon-2 has increased expressiveness and safety. Oberon-2 also "adds simplicity", because there are

no subranges, which are no longer needed for array index range declarations, because array bounds generally start at 0
no enumerations
no unsigned type (CARDINAL)
no nested modules, which did not add any functionality
no variant records, which are replaced by the safer concept of extensible records
no WITH-statement of the Modula-2 language, which had many disadvantages in respect to program readability and thus severed maintainability
no qualified import, i.e. imported identifiers must be qualified with the module name or its alias
no separate definition- and implementation-module

The latter saves a great deal of software maintenance, since the interface specification of a module is generated by a tool from the symbol file. Subranges and unsigned types in Modula-2 complicated the whole-number type compatibility rules without adding any important functionality. Program language design is a compromise and it is disputable, whether enumeration types increase readability or static program safety. This is an often discussed feature, but the least important. If the goal is to make a language as simple a possible and given that they do not add functionality, enumeration types are not required.

Oberon-2 main features

integer type hierarchy
objects, called extensible records
polymorphic types and single inheritance; methods are simply type bound procedures
type test and type guard
dynamic arrays, allocated on the heap, where the array index range can be determined at run-time
read-only export
import module name alias

Persistent objects and meta-programming facilities are supported via a library module.

As an advantage over Modula-2, Oberon-2 features save pointers under the provision that SYSTEM.ADR and type casting SYSTEM.VAL is not used. All pointer variables, even when declared within a structured type, be it global, local, or heap are inititialised to NIL and there is no DISPOSE (although stand-alone implementation without garbage collector might allow to use Objects.DISPOSE).

Run-time check of a pointer type is done via so-called type descriptors and pointer type tags for both, static and dynamic objects.

Oberon-2 is simpler, but more powerful than Modula-2.

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Comparison of Oberon-2 with Modula-2

Oberon-2 main features

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