3 ms·

would it be fair to say you have just described references, or do I have to go and lookup this algol/mesa stuff?

pjmlp 12y ago
I can provide a better example, but only tonight. At work now.
pjmlp 12y ago
Some examples using Modula-2, a Mesa's successor. How it allows for all the C pointer features, while adding a little bit more safety. MODULE examples; IMPORT Terminal, SYSTEM; (* procedure with reference parameter, no need for pointers *) PROCEDURE ChangeParam (VAR changeMe: CARDINAL); BEGIN changeMe := 25; END ChangeParam; (* procedure with a slice, bounds given by HIGH(changeMe) and LOW(changeMe). also a string in this case no need for explicit pointers *) PROCEDURE DumpLetters (VAR letters: ARRAY OF CHAR); VAR i : CARDINAL; BEGIN FOR i := 0 TO HIGH(letters) DO WriteChar(letters[i]); WriteLn; (* Or just use *) WriteString (letters); END DumpLetters; VAR anInt : CARDINAL := 12 ; aPtr : POINTER TO CHAR; aBuffer : ARRAY [1..2] OF CHAR; anAddr : ADDRESS; (* think void* *) aPtr2 : POINTER TO CHAR; BEGIN WriteInt(anInt); (* writes 12 *) ChangeParam (anInt); WriteInt(anInt); (* writes 25 *) DumpLetters ('A simple string'); NEW(aPtr); (* The compiler knows the size, no need for sizeof, but you can use ALLOCATE(aPTR, SIZE(CHAR)) if you want *) (* This is where it shares the same problems with C, due to manual memory control *) DISPOSE(aPtr); (* do pointer arithmetic if really required *) anAddr := SYSTEM.ADDADR (SYSTEM.ADR(aBuffer), SIZE(CHAR) * 1); aPtr2 := SYSTEM.CAST(POINTER TO CHAR, anAddr); (* aPtr2 now points to aBuffer(2) *) END examples; So the compiler will mark this module as unsafe since the meta-package SYSTEM is being used. All Modula-2 successors, have GC support, as such the DISPOSE() would have to be written as SYSTEM.DISPOSE() and could only be applied to untraced pointers.
- throwawayaway 12y ago
  very interesting, reminds me of this: http://stackoverflow.com/questions/6456253/why-is-reference-to-array-defined-in-such-confusing-way-in-c http://stackoverflow.com/questions/6456253/why-is-reference-... it's a great shame it's defined in such an alien to use way in C++.

pjmlp 12y ago

I can provide a better example, but only tonight. At work now.

pjmlp 12y ago

Some examples using Modula-2, a Mesa's successor. How it allows for all the C pointer features, while adding a little bit more safety. MODULE examples; IMPORT Terminal, SYSTEM; (* procedure with reference parameter, no need for pointers *) PROCEDURE ChangeParam (VAR changeMe: CARDINAL); BEGIN changeMe := 25; END ChangeParam; (* procedure with a slice, bounds given by HIGH(changeMe) and LOW(changeMe). also a string in this case no need for explicit pointers *) PROCEDURE DumpLetters (VAR letters: ARRAY OF CHAR); VAR i : CARDINAL; BEGIN FOR i := 0 TO HIGH(letters) DO WriteChar(letters[i]); WriteLn; (* Or just use *) WriteString (letters); END DumpLetters; VAR anInt : CARDINAL := 12 ; aPtr : POINTER TO CHAR; aBuffer : ARRAY [1..2] OF CHAR; anAddr : ADDRESS; (* think void* *) aPtr2 : POINTER TO CHAR; BEGIN WriteInt(anInt); (* writes 12 *) ChangeParam (anInt); WriteInt(anInt); (* writes 25 *) DumpLetters ('A simple string'); NEW(aPtr); (* The compiler knows the size, no need for sizeof, but you can use ALLOCATE(aPTR, SIZE(CHAR)) if you want *) (* This is where it shares the same problems with C, due to manual memory control *) DISPOSE(aPtr); (* do pointer arithmetic if really required *) anAddr := SYSTEM.ADDADR (SYSTEM.ADR(aBuffer), SIZE(CHAR) * 1); aPtr2 := SYSTEM.CAST(POINTER TO CHAR, anAddr); (* aPtr2 now points to aBuffer(2) *) END examples; So the compiler will mark this module as unsafe since the meta-package SYSTEM is being used. All Modula-2 successors, have GC support, as such the DISPOSE() would have to be written as SYSTEM.DISPOSE() and could only be applied to untraced pointers.

throwawayaway 12y ago
very interesting, reminds me of this: http://stackoverflow.com/questions/6456253/why-is-reference-to-array-defined-in-such-confusing-way-in-c http://stackoverflow.com/questions/6456253/why-is-reference-... it's a great shame it's defined in such an alien to use way in C++.