[M3devel] operator overloading?

[Mika Nystrom]

I don't like changes in Modula-3, on principle.  I have a lot of code
that is over ten years old and that I never look at, and I never want
to look at, despite the fact that things that I do depend on computers
that execute probably billions of instructions in this code every day.

Now I depend on such code that depends on being able to parse
Modula-3 itself, so the language, I feel should stay both forward-
and backward-compatible.  (I really don't like LONGINT for that
reason.)

But that being said, operator overloading seems relatively harmless.
It changes the meaning only of executable code, not interfaces, and unless
you are writing a compiler, there isn't much reason to be processing
the executable code.  This is all assuming you do it right.  And there
must be some way of calling the overloaded operators using functional
notation so that generated code can get at them.

What has always bugged me about operator overloading in C++ is just
what an unabashed hack it is.  You can use the operators from C,
but no others?  And they have to have the same associativity and
commutativity rules as in C?  And they can be only unary or binary?
Does anyone do this better?  Is it even possible?  I suppose the main
thing is to specify a rule for converting 

a OP b

to 

OP(a,b)...

What does C++ do?  Make it a.OP(b)?  The asymmetry is really ugly.  And
then the associativity rules... is addition left- or right-associative?
Who remembers that..? now *that* is obscure.  And it won't work on RECORDs
or ARRAYs or SETs, which don't have methods...

Would it be possible to write a pre-processor using m3tk that would
implement the entirety of operator overloading?  I think that would
be an elegant solution, but I've never used m3tk on implementations...
The reason I am saying this is that judging from the syntax equations
in the Green Book, it is possible that m3tk might accept a program using
overloaded operators, and only semantic analysis on the parsed structure
would uncover the overloaded operators and flag them as semantic errors
(in standard Modula-3).  But I might be wrong.  And m3tk might have
broken code in it.  

When we were designing async. hardware with Modula-3 we had a thing
called "m3texthack" that would let you do special kinds of macros in
Modula-3 code.  Your source file would be Module.c3, which would
be pre-processed into Module.m3 by m3texthack (all handled by m3build/cm3
of course).

In any case, an m3tk solution rather than a Modula-3 solution would easily
allow you to specify different rules for different types, or even for
different source files, rather than being tied to something nailed down
in the language spec.

     Mika



Jay K writes:
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>"Obscures the underlying code" is true of so many things.
>Exceptions. Garbage collection. Objects. Nested functions. Function calls! =
>Default parameters. Generics. Pickles. RPC.
>It is a matter of degree=2C cost=2C value though=2C granted.
>  The runtime cost of operating overloading is zero=2C at least.
>  And the unobscured code is horrible to read and write actually (which is =
>the reason for many features).
>  This is case where "obscure" is clearly good=2C and not obscure.
>  But it is a matter of degree. I should probably try implementing it befor=
>e I ask for it too strongly.
>
>
>  - Jay
>
>From: hosking at cs.purdue.edu
>Date: Sun=2C 21 Nov 2010 13:33:31 -0500
>To: jay.krell at cornell.edu
>CC: m3devel at elegosoft.com
>Subject: Re: [M3devel] operator overloading?
>
>
>
>Some of us find operator overloading anathema because it obscures the actua=
>l underlying code.It certainly does not fit well with the design philosophy=
> of Modula-3.
>
>On Nov 21=2C 2010=2C at 1:10 PM=2C Jay K wrote:Is it really so difficult to=
> add operator overloading to the language?
>
>>From a user's point of view=2C I know it is very useful in certain situatio=
>ns.
>
>
> - Jay
>
>
>
>
>
> 		 	   		  =
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>"Obscures the underlying code" is true of so many things.<br>Exceptions. Ga=
>rbage collection. Objects. Nested functions. Function calls! Default parame=
>ters. Generics. Pickles. RPC.<br>It is a matter of degree=2C cost=2C value =
>though=2C granted.<br>&nbsp=3B The runtime cost of operating overloading is=
> zero=2C at least.<br>&nbsp=3B And the unobscured code is horrible to read =
>and write actually (which is the reason for many features).<br>&nbsp=3B Thi=
>s is case where "obscure" is clearly good=2C and not obscure.<br>&nbsp=3B B=
>ut it is a matter of degree. I should probably try implementing it before I=
> ask for it too strongly.<br><br><br>&nbsp=3B - Jay<br><br><hr id=3D"stopSp=
>elling">From: hosking at cs.purdue.edu<br>Date: Sun=2C 21 Nov 2010 13:33:31 -0=
>500<br>To: jay.krell at cornell.edu<br>CC: m3devel at elegosoft.com<br>Subject: R=
>e: [M3devel] operator overloading?<br><br>
><meta http-equiv=3D"Content-Type" content=3D"text/html=3B charset=3Dunicode=
>">
><meta name=3D"Generator" content=3D"Microsoft SafeHTML">Some of us find ope=
>rator overloading anathema because it obscures the actual underlying code.<=
>div>It certainly does not fit well with the design philosophy of Modula-3.<=
>br><div><br><div><div>On Nov 21=2C 2010=2C at 1:10 PM=2C Jay K wrote:</div>=
><br class=3D"ecxApple-interchange-newline"><blockquote><span class=3D"ecxAp=
>ple-style-span" style=3D"border-collapse: separate=3B font-family: Helvetic=
>a=3B font-style: normal=3B font-variant: normal=3B font-weight: normal=3B l=
>etter-spacing: normal=3B line-height: normal=3B text-indent: 0px=3B text-tr=
>ansform: none=3B white-space: normal=3B word-spacing: 0px=3B font-size: med=
>ium=3B"><div class=3D"ecxhmmessage" style=3D"font-size: 10pt=3B font-family=
>: Tahoma=3B">Is it really so difficult to add operator overloading to the l=
>anguage?<br><br>From a user's point of view=2C I know it is very useful in =
>certain situations.<br><br><br>&nbsp=3B- Jay<br><br><br><br><br></div></spa=
>n></blockquote></div><br></div></div> 		 	   		  </body>
></html>=
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