Re: Can you constrain a type based on properties of what it is being referenced by?
On 2/2/18 9:19 AM, aliak wrote:
To further explain what I mean:
struct A if (!is(this == immutable) && !is(this == shared))
{
}
shared a = A() // error
auto a = A() // ok
immutable a = A() // error
const a = A() // ok
In this case, no. A struct is bit-copyable, so you must be able to move
it bit-by-bit to another copy.
In the case of attribute addition or removal, the compiler allows
anything as long as there are no reference types contained in the
struct. Your example has no members, which means no references, so it's
a value type.
If you put a pointer inside your struct, you will get the behavior you
are looking for I think. However, you may have to disable the
constructor for your exact requirements above.
-Steve
Re: Can you constrain a type based on properties of what it is being referenced by?
On Friday, 2 February 2018 at 14:19:37 UTC, aliak wrote: ... (see post in general forum by Simon for details [1]) *Simen Gah! Sorry!
Can you constrain a type based on properties of what it is being referenced by?
To further explain what I mean:
struct A if (!is(this == immutable) && !is(this == shared))
{
}
shared a = A() // error
auto a = A() // ok
immutable a = A() // error
const a = A() // ok
Fake syntax above of course.
I was thinking about this because I read a few posts about const,
and approaching it via allowing an object to define a head
mutable version of itself (see post in general forum by Simon for
details [1])
And there're few constructs like RefCounted which don't make
sense with an immutable qualifier.
And then there're situations where a mutable version does not
make sense (I think this would be a much bigger application), ie:
handles, resource identifiers, application configuration details,
etc.
[1]
https://forum.dlang.org/thread/cpxfgdmklgusodqou...@forum.dlang.org
