Eberon Strings

A new basic type STRING is introduced because oberon has nothing to deal with strings of arbitrary length. Any possible library solution will have a lot of syntax noise and have no chance to optimize trivial string operations. Oberon is not C++ with all these complex things (like operator overloading etc.) which make library solution viable so it is simplier to just support a new basic type on compiler level.

Semantics

STRING is a basic type. It represents a sequence of characters of any length (including zero - empty string). STRING is very similar to ARRAY OF CHAR:

• STRING can be indexed [] as CHAR
• predefined procedure LEN returns the length of STRING
• STRING can be compared
• STRING can be assigned from string literal
• STRING can be passed as open non-VAR ARRAY OF CHAR

But also there are differences:

• STRING content is read-only, it never modified
• ARRAY OF CHAR cannot be assigned to STRING or passed as STRING
• STRING can be returned as a result of procedure

STRING supports concatenation through '+' operator. Also '+' is supported for string literals:

Example:

CONST constString = 22X + "abc" + 22X;
VAR s: STRING;
...
s := s + constString + s;

STRING default value is empty string - "". STRING cannot be NIL.

All special cases described in original Wirth report regarding to ARRAY OF CHAR (comparing to other array types) seem not actual after introducing a separate type STRING to support strings but they are left as is in Eberon to maintain compatibility with original oberon.