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digitalmars.D - in vs. const

reply dsimcha <dsimcha yahoo.com> writes:
All the discussion about const on this NG lately has made me realize that I
have no idea what the difference is between const and in, i.e. what is the
difference between:

SomeType foo(const SomeType bar) and
SomeType foo(in SomeType bar)

?
Mar 07 2009
next sibling parent reply Sean Kelly <sean invisibleduck.org> writes:
dsimcha wrote:

 All the discussion about const on this NG lately has made me realize that I
 have no idea what the difference is between const and in, i.e. what is the
 difference between:
 
 SomeType foo(const SomeType bar) and
 SomeType foo(in SomeType bar)


There's no difference between them.  The 'in' version just happens to be 
D1-compatible, and its meaning could be more easily changed over time if 
any tweaking is necessary (unlikely).
Mar 07 2009
parent reply Adam Burton <adz21c googlemail.com> writes:
Sean Kelly wrote:


 dsimcha wrote:

 All the discussion about const on this NG lately has made me realize that
 I have no idea what the difference is between const and in, i.e. what is
 the difference between:
 
 SomeType foo(const SomeType bar) and
 SomeType foo(in SomeType bar)


 
 There's no difference between them.  The 'in' version just happens to be
 D1-compatible, and its meaning could be more easily changed over time if
 any tweaking is necessary (unlikely).


I have not done any D2, but surely 'in' is modifiable in the function locally 
where as const is not (so since const is not modifiable at all it implies 
in).
For example:

void myfunc(in int i)
{
	i = 10;	// i is changed to 10, k stays as 12
}

int k = 12;
myfunc(k);	

=================================

void myfunc(const int i)
{
	i = 10;	// Fails to compile as i is const
}

in k = 12;
myfunc(k);
Mar 07 2009
parent reply Robert Fraser <fraserofthenight gmail.com> writes:
Adam Burton wrote:

 Sean Kelly wrote:
 

 dsimcha wrote:

 All the discussion about const on this NG lately has made me realize that
 I have no idea what the difference is between const and in, i.e. what is
 the difference between:

 SomeType foo(const SomeType bar) and
 SomeType foo(in SomeType bar)


 There's no difference between them.  The 'in' version just happens to be
 D1-compatible, and its meaning could be more easily changed over time if
 any tweaking is necessary (unlikely).


 I have not done any D2, but surely 'in' is modifiable in the function locally 
 where as const is not (so since const is not modifiable at all it implies 
 in).
 For example:
 
 void myfunc(in int i)
 {
 	i = 10;	// i is changed to 10, k stays as 12
 }
 
 int k = 12;
 myfunc(k);	
 
 =================================
 
 void myfunc(const int i)
 {
 	i = 10;	// Fails to compile as i is const
 }
 
 in k = 12;
 myfunc(k);
 


No it's not. "in" means "const scope" in D2 (and scope is a NOP right now).
Mar 07 2009
parent Sergey Gromov <snake.scaly gmail.com> writes:
Sat, 07 Mar 2009 17:43:19 -0800, Robert Fraser wrote:


 Adam Burton wrote:

 Sean Kelly wrote:
 

 dsimcha wrote:

 All the discussion about const on this NG lately has made me realize that
 I have no idea what the difference is between const and in, i.e. what is
 the difference between:

 SomeType foo(const SomeType bar) and
 SomeType foo(in SomeType bar)


 There's no difference between them.  The 'in' version just happens to be
 D1-compatible, and its meaning could be more easily changed over time if
 any tweaking is necessary (unlikely).


 I have not done any D2, but surely 'in' is modifiable in the function locally 
 where as const is not (so since const is not modifiable at all it implies 
 in).
 For example:
 
 void myfunc(in int i)
 {
 	i = 10;	// i is changed to 10, k stays as 12
 }
 
 int k = 12;
 myfunc(k);	
 
 =================================
 
 void myfunc(const int i)
 {
 	i = 10;	// Fails to compile as i is const
 }
 
 in k = 12;
 myfunc(k);
 


 
 No it's not. "in" means "const scope" in D2 (and scope is a NOP right now).


Closures are not allocated for delegates passed as scope arguments so
scope is far from NOP.
Mar 08 2009
prev sibling next sibling parent Sergey Gromov <snake.scaly gmail.com> writes:
Sat, 7 Mar 2009 15:37:07 +0000 (UTC), dsimcha wrote:


 All the discussion about const on this NG lately has made me realize that I
 have no idea what the difference is between const and in, i.e. what is the
 difference between:
 
 SomeType foo(const SomeType bar) and
 SomeType foo(in SomeType bar)
 
 ?


In D1, there are no const types, so the first form doesn't compile.  In
the second form 'in' is redundant,  it means the default behavior and
may be omitted without consequences.

In D2, 'in' means 'const scope'.  I've seen that in writing but can't
remember where.

Therefore clever people use 'in' to mean 'const' in D2 and NOP in D1 to
improve portability.
Mar 07 2009
prev sibling parent reply Kagamin <spam here.lot> writes:
Sergey Gromov Wrote:


 In D2, 'in' means 'const scope'.  I've seen that in writing but can't
 remember where.


How can it be scope? If you have scope object, it gets *destructed* when
leaving scope: when function exits. Ouch.
Mar 09 2009
parent reply "Denis Koroskin" <2korden gmail.com> writes:
On Mon, 09 Mar 2009 18:07:05 +0300, Kagamin <spam here.lot> wrote:


 Sergey Gromov Wrote:


 In D2, 'in' means 'const scope'.  I've seen that in writing but can't
 remember where.


 How can it be scope? If you have scope object, it gets *destructed* when  
 leaving scope: when function exits. Ouch.


No. Scope has different meaning here. For example, delegates don't cause heap
allocation when passed as scope parameters in D2.
Mar 09 2009
parent Kagamin <spam here.lot> writes:
Denis Koroskin Wrote:


 No. Scope has different meaning here.


O RLY? That's good news.
Mar 09 2009