[Oberon] ARRAY OF CHAR mystery

spir denis.spir at gmail.com
Tue Jun 22 16:05:19 MEST 2010


In an attempt to build a string abstraction as evoked in the previous theread, I'm blocked with the following issue:

I find myself unable to assign an ARRAY OF CHAR value to an ARRAY OF CHAR variable. Below pchars is of type POINTER TO ARRAY OF CHAR. The statement
    pchars^ := chars;
is refused. Below results of compilation with oo2c and obc:

oo2c --make "trial.Mod" (in directory: /home/spir/prog/oberon)
Compilation failed.
/home/spir/prog/oberon/trial.Mod:16:15: Expression not compatible with variable type `ARRAY'

obc  "trial.m" (in directory: /home/spir/prog/oberon)
Compilation failed.
"trial.m", line 16: type ARRAY OF CHAR is needed on the RHS of this assignment
> 	pchars^ := chars;
> 	         ^^^^^
> This expression has type ARRAY OF CHAR

obc's message is very nice ;-)

A side issue is that I cannot find another way to return an array or a record other than via a pointer. Meaning eg a Text type would actually need to be a type of pointers to actual string data. But pointers break clear and secure value semantics, in that after
	t2 := t1;
any change to either text affects both. One is thus forced to explicitely dereference all string variables:
	t2^ := t1^;

I also find myself forced to build the string data self as a record to be able to affect it various needed methods. So, I end up as of now with the following:

	PChars	= POINTER TO Chars;
	DText	= RECORD		(* actual text data *)
		pchars	: PChars;
		count	: LONGINT;
		isEmpty	: BOOLEAN;
	Text	= POINTER TO DText;

But I'm blocked, as explained above, in assigning pchars^ at creation of a Text.


vit esse estrany ☣


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