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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).

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)

D1-compatible, and its meaning could be more easily changed over time if any tweaking is necessary (unlikely).

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)

D1-compatible, and its meaning could be more easily changed over time if any tweaking is necessary (unlikely).

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 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