• Robin (20/20) Feb 08 2015 Hiho,
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (17/20) Feb 08 2015 Post-increment cannot be overloaded in D. It is always implemented in
• Robin (4/4) Feb 08 2015 Thank you for your reply. I didn't know that it isn't possible to

"Robin" <robbepop web.de> writes:

Hiho,

as I am currently very insterested in compiler implementation I 
often look into the DMD github and look how things are done 
there. Often I find myself curious about things at first but find 
out the rational behind certain implementation decisions.

One thing I can't figure out is the different approach with pre- 
and postfix expressions. While prefix expressions inherit from 
UnaExp (unary expression) which makes sense to me as it is an 
expression with only one parameter (in general) the postfix inc 
and decrement expressions are inherited from BinExpr (binary 
expression) which define their second expression to be an integer 
expression with a value of 1.

So I am very curious about the rational behind this design 
decision. Why do Postfix expression not inherit from UnaExp, too? 
Am I missing something very important?

Thanks in advance! =)

I hope this is the right place to ask questions about the DMD 
compiler.

Regards,
Robin

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 02/08/2015 01:05 PM, Robin wrote:

 the postfix inc and decrement expressions are
 inherited from BinExpr (binary expression) which define their second
 expression to be an integer expression with a value of 1.

Post-increment cannot be overloaded in D. It is always implemented in 
terms of pre-increment (or +=):

   http://dlang.org/operatoroverloading.html

Although I can't find it on the spec, I think it used to be spelled out 
that pre-increment (and post-increment) could be the equivalent of "+= 
1". I am pretty sure about that because my notes say so! :p (because I 
based everything on what I knew to be correct at the time).

   http://ddili.org/ders/d.en/operator_overloading.html

Quoting myself:

"if an opBinary overload supports the duration += 1 usage, then opUnary 
need not be overloaded for ++duration and duration++. Instead, the 
compiler uses the duration += 1 expression behind the scenes. Similarly, 
the duration -= 1 overload covers the uses of --duration and duration-- 
as well."

Perhaps that's why the compiler uses a binary operator for post-increment.

Ali

"Robin" <robbepop web.de> writes:

Thank you for your reply. I didn't know that it isn't possible to 
overload the post-inc and decrement operators in Dlang but I 
think I don't even miss this feature if pre-inc/dec is still 
available. =)