On Tuesday, 26 May 2015 at 21:22:38 UTC, Per Nordlöw wrote:
No, DMD cannot currently handle scope on foreach elements. It
errors as
Error: basic type expected, not scope
Quite possible, didn't test it. Anyway, my point was that it
simply isn't necessary to ever mark a local variable as `scope`.
The compiler sees all local variables and can figure things out
by itself. It only needs help in function signatures, in the form
of explicit `scope` and `return` annotations.
example, it would figure out that you're assigning a reference
to a value with shorter lifetime (i.e. the slice to the
buffer) to a value with longer lifetime (saved_line), which it
would disallow. (Btw, I don't think to!string is enough,
because it is probably a no-op in this case: string -> string).
No to!string is not a no-op in this case. It allocates but it
needs to create an immutable char array that is: char[] ->
string
I see, File.byLine returns a range of char[], I thought it
returned a string range. Then you're of course right.
However, byLine has another problem, which boils down to the
same cause as the problem with RCArray, namely that the
content of the buffer is reused in each iteration.
This is what I meant with volatile. Is there a better word for
this?
I guess it's fine, and now I remember again that ranges with this
property have been called "volatile ranges".
the "owner" can be modified while references to it exist. For
byLine, this is not a safety violation, but for RCArray it is.
A solution applicable to both is to detect this and then
either treat such a situation as @system, or make the owner
`const` as long as the references are alive.
AFAIK: Allowing scope in foreach would solve this problem in my
case.
See above. Conceptually, you can of course treat it as if it were
marked with `scope`, but an actual annotation should not be
necessary.
