On 02/04/2013 11:18 PM, Andrei Alexandrescu wrote:
On 2/4/13 10:30 PM, Chad Joan wrote:
I agree with Jonathan.
Please do not make them a subset. Make them as identical as possible.
The subset thing makes them no longer "swappable". Allow variables to be
marked with @property to limit them to operations that @property
functions can do, and make sure @property functions are limited to what
@property variables can do (ex: no address-of!). With that in hand,
they'll be very swappable.
The purpose is to replace members with properties, not to change one's
mind back and forth. There will be no marking of variables with
@property as that can be easily achieved by actually making them
properties.
Andrei
Related:
Is there some reason why we /need/ to be able to take the address of
properties?
Wouldn't something like 'someFunc(PropAccessor!"prop"(foo))' work in
cases where we need a generic way to defer reads and writes?
For clarity:
auto PropAccessor(string propertyStr, T)( T tinstance )
{
struct Accessor(string propertyStr, U)
{
private U tinstance;
auto get()
{
mixin("return tinstance."~propertyStr~";");
}
// I had to put @system here to shut up a compiler error. Bug?
@system void set(V)(V val)
{
mixin("tinstance."~propertyStr~" = val;");
}
}
Accessor!(propertyStr, T) acc;
acc.tinstance = tinstance;
return acc;
}
auto PtrAccessor(T)( T* payload )
{
struct Accessor(U)
{
private U* payload;
U get()
{
return *payload;
}
U set(U val)
{
return *payload = val;
}
}
Accessor!(T) acc;
acc.payload = payload;
return acc;
}
template isAccessor(Acc)
{
Acc a;
static if (
__traits(compiles, { auto x = a.get(); } ) &&
__traits(compiles, a.set(a.get())) )
const bool isAccessor = true;
else
const bool isAccessor = false;
}
// Function that accepts the be-all-end-all of reference types.
auto someFunc(Acc)(Acc qux) if ( isAccessor!(Acc) )
{
auto x = qux.get();
x |= 0xF00D;
qux.set(x);
return qux.get();
}
struct MyStruct
{
private int m_q;
@property int q() { return m_q; }
@property void q(int v) { m_q = v; }
}
unittest
{
MyStruct s;
s.q = 0;
int abc = 0;
assert(someFunc(PtrAccessor(&abc)) == 0xF00D);
assert(someFunc(PropAccessor!"q"(s)) == 0xF00D);
}
void main()
{
}
