On 06/20/2012 01:36 PM, Christophe Travert wrote:
Timon Gehr , dans le message (digitalmars.D:170288), a écrit :
On 06/20/2012 09:16 AM, deadalnix wrote:
Le 19/06/2012 17:49, Timon Gehr a écrit :
The question is, what the meaning of 'const' references should be:
1. data cannot be changed transitively through the reference
2. the reference can reference both 'const' and 'immutable' data and
'immutable' data can transitively not be changed through the
reference.
1. requires transitive const for delegate context pointers, 2. does not.
No, 2. require 1., even if the initialization is broken.
class Foo {
void delegate() dg;
this(immutable void delegate() dg) immutable {
thid.dg = dg;
}
}
Now, as delegate doesn't carry the constness of its context, an
immutable instance of Foo can refers to something that isn't immutable.
Clarification: 'const' means 'const'. No other qualifiers.
There is no 'const' in that example code. 'immutable' obviously needs to
be transitive regardless of the particular interpretation of 'const'.
const means: maybe immutable.
Or maybe mutable. Therefore, interpretation '2.'
Thus const needs to be transitive too.
Wrong. This is the (A==>B) ==> (B==>A) fallacy, where
A: 'const' is transitive
B: 'const' references cannot modify 'immutable' data
The conclusion regarding transitivity, given interpretation 2., is that
'const' needs to be transitive _if_ it is actually 'immutable'.
If you apply different rules to const and to immutable, you are breaking
the consistency of the langage.
Certainly not. This is like saying that applying different rules to
'const' and mutable is breaking the consistency of the language.
mutable is not transitive.
