Luther Tychonievich wrote:
Stewart Gordon Wrote:
That leaves AAs to consider....
I can't find any conceptual difference here between any type of
indirection: pointers, "ref" variables, static arrays, dynamic
arrays, associative arrays, even aggregate types if the typing engine
bothered with them:
Static arrays aren't a type of indirection. They have value semantics.
Hence const(char[26]) and const(char)[26] are identical. (There seems
to be a bug at the moment whereby DMD treats them as different types.)
<snip>
Associative arrays are conceptually aggregates of two types (key and
value), and both should follow the safe upcasting rules; in practice,
however, the implementation (at least dmd 2.022) automatically
const-s all but the outermost level of indirection within the key
type, such that "int[int[]]" parses as "int[const(int)[]]", so the
rule will never rule out a key type.
So effectively, key types are implicitly tail-consted.
(incidentally, I just noticed that the AA initializer expression
"[[1]:2]" won't parse in dmd...)
There may be some subtleties to the "all objects are implicitly
pointers" rule (implying that class types are a kind of indirection),
but at first glance they seem to be avoided because const-ness cannot
get inside that implicit pointer.
Indeed, classes used as AA keys seem to be mutable by default. But this
does seem to be an inconsistency.
There is std.typecons.Rebindable. But ISTM mainly a syntax deficiency
that this can't be expressed as a D builtin.
Stewart.
