On Wednesday, 31 August 2016 at 10:12:21 UTC, Johannes Pfau wrote:
There was @disable this(this)
This prevents to use a location as argument to a function,
like:
print(timer.count). Is there any reason to have this line or
not?
I guess timer is a (enum) pointer to a struct and count is a
Volatile!T
field in that struct?
Yes
But then timer.count does not return a address, it returns the
value of
count? Unless of course print(X) takes its argument by ref or
alias.
I want to use them just by value.
The reason for @disable this(this) is to disable copying of the
struct.
The compiler otherwise accesses T raw in a 'non-volatile' way
when
copying the value. In D we can only have a postblit function,
but we
cannot reimplement the copying. opAssign can only be used in
some cases:
Foo f;
auto f2 = Foo();
auto f3 = f2;
f = Foo();
f = f2;
Only the last two lines call opAssign. So "auto f3 = f2" could
copy a Volatile!T in a non-volatile way. This is the reason for
@disable this(this), AFAIK.
I think I somehow get the point even if I do not fully understand
the explanation.
But it is too restrictive if I always need to have a getter
function or assign the value first to a temporary variable to use
the value in a function call.
Anyway, I think it is a gdc bug that the error message comes from
the called function that has nothing to do with this. The error
should show the function call where the disabled copy operation
is.
