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digitalmars.D - ? valid opAssign

reply Thomas Kuehne <thomas-dloop kuehne.thisisspam.cn> writes:
Is the code below valid? 

# int main(){
#	int a=2;
#	int b;
#	return b=b=a;
# }

The reason I ask is that this code passes the compiler,
but I can't find and documentation on it's behaviour.

Thomas
Nov 16 2004
parent reply Daniel Keep <daniel.keep dummy.gmail.com> writes:
Ok, I could be wrong, BUT, I think that it's valid.

The trick here is that (unless Walter changed it from C/C++), assignment 
can be used in an expression.  Specifically, (a=b) first assigns the 
value of b to a, then returns a.

So `return b=b=a;' is assigning a to b, b to itself, then returning the 
value of b.

Maybe :P

	-- Daniel

Thomas Kuehne wrote:

 Is the code below valid? 
 
 # int main(){
 #	int a=2;
 #	int b;
 #	return b=b=a;
 # }
 
 The reason I ask is that this code passes the compiler,
 but I can't find and documentation on it's behaviour.
 
 Thomas
Nov 16 2004
parent reply Regan Heath <regan netwin.co.nz> writes:
On Tue, 16 Nov 2004 19:11:30 +1100, Daniel Keep 
<daniel.keep dummy.gmail.com> wrote:


 Ok, I could be wrong, BUT, I think that it's valid.

 The trick here is that (unless Walter changed it from C/C++), assignment 
 can be used in an expression.  Specifically, (a=b) first assigns the 
 value of b to a, then returns a.

 So `return b=b=a;' is assigning a to b, b to itself, then returning the 
 value of b.



Or, is the order reversed, i.e. assigns b to b, then a to b.
Of course in both cases the result is the same, b=a.
The real question is, is the order defined?
If so, what is it?

Regan


 Thomas Kuehne wrote:

 Is the code below valid? # int main(){
 #	int a=2;
 #	int b;
 #	return b=b=a;
 # }

 The reason I ask is that this code passes the compiler,
 but I can't find and documentation on it's behaviour.

 Thomas








-- 
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/
Nov 16 2004
parent Daniel Keep <daniel.keep dummy.gmail.com> writes:
Hmm... my intuition tells me it's right to left.  Assignment *should* be 
right associative--it computes the right hand side first (thus, 
performing all the assignments right to left).

But then again, IANALL

Regan Heath wrote:

 On Tue, 16 Nov 2004 19:11:30 +1100, Daniel Keep 
 <daniel.keep dummy.gmail.com> wrote:
 

 Ok, I could be wrong, BUT, I think that it's valid.

 The trick here is that (unless Walter changed it from C/C++), 
 assignment can be used in an expression.  Specifically, (a=b) first 
 assigns the value of b to a, then returns a.

 So `return b=b=a;' is assigning a to b, b to itself, then returning 
 the value of b.



 
 Or, is the order reversed, i.e. assigns b to b, then a to b.
 Of course in both cases the result is the same, b=a.
 The real question is, is the order defined?
 If so, what is it?
 
 Regan
 

 Thomas Kuehne wrote:


 Is the code below valid? # int main(){
 #    int a=2;
 #    int b;
 #    return b=b=a;
 # }

 The reason I ask is that this code passes the compiler,
 but I can't find and documentation on it's behaviour.

 Thomas
Nov 17 2004