digitalmars.D - refRange and disable this(this);
- Jerry (30/30) Sep 14 2016 I got a range which disables copy construction and I want to loop
- Jerry (3/5) Sep 14 2016 Or more specificly, shouldn't save only be defined if the range
- Jonathan M Davis via Digitalmars-d (22/50) Sep 14 2016 It's opAssign does a copy. The rationale is given in its documentation:
- Mathias Lang via Digitalmars-d (6/34) Sep 14 2016 You should be able to work around this by using `for` loop instead of
- Jacob Carlborg (17/45) Sep 15 2016 As a workaround you can take the address of the range and use
I got a range which disables copy construction and I want to loop
the range within another loop using the same range.
So I thought I can mark the struct range with disable this(this)
and then use refRange to initialize the loop.
So with something like this:
void main()
{
auto valueRange = FooRange("123");
foreach(ch; refRange(&valueRange))
writeln(ch);
}
struct FooRange {
disable this();
disable this(this);
this(string str) {
this.str = str;
}
property bool empty() { return str.empty; }
property dchar front() { return str.front; }
void popFront() { str.popFront; }
private:
string str;
}
But I get compile time errors messages saying:
std/range/package.d(8155,23): Error: struct app.FooRange is not
copyable because it is annotated with disable
It feels strange that refRange ever want to copy.
Bug or feature?
Sep 14 2016
Jerry <Kickupx gmail.com> On Wednesday, 14 September 2016 at 12:39:16 UTC, Jerry wrote:It feels strange that refRange ever want to copy. Bug or feature?Or more specificly, shouldn't save only be defined if the range defines it instead of using copy? Which is presume is the problem.
Sep 14 2016
On Wednesday, September 14, 2016 12:39:16 Jerry via Digitalmars-d wrote:
I got a range which disables copy construction and I want to loop
the range within another loop using the same range.
So I thought I can mark the struct range with disable this(this)
and then use refRange to initialize the loop.
So with something like this:
void main()
{
auto valueRange = FooRange("123");
foreach(ch; refRange(&valueRange))
writeln(ch);
}
struct FooRange {
disable this();
disable this(this);
this(string str) {
this.str = str;
}
property bool empty() { return str.empty; }
property dchar front() { return str.front; }
void popFront() { str.popFront; }
private:
string str;
}
But I get compile time errors messages saying:
std/range/package.d(8155,23): Error: struct app.FooRange is not
copyable because it is annotated with disable
It feels strange that refRange ever want to copy.
Bug or feature?
It's opAssign does a copy. The rationale is given in its documentation:
The result of that is that the range you give it needs to be copyable. But
the reality of the matter is that ranges in general expect to be copyable,
and range-based code is going to have a tendency to fall flat on its face if
you try to define a range that's non-copyable. I'm actually kind of
surprised that such a range passes isInputRange given that it tests this
line:
R r = R.init;
But I guess that it works, because you didn't explicitly disable opAssign
(though at least sometimes, disabling the postblit constructor seems to
disable opAssign from what I recall).
If want to guarantee that a range's state is never copied, and you're
creating a range specifically for this, you might as well just make it a
class and force it to have reference semantics. RefRange was intended for
cases where you have a range that works normally, but you need to pass it to
some code and have the the state of the range be updated rather than having
a copy updated. It wasn't intended that it be used for a range that you
wanted to always be a reference type, since if you want that, you can just
declare a range that's a reference type.
- Jonathan M Davis
Sep 14 2016
You should be able to work around this by using `for` loop instead of
`foreach`.
IMO that's a design bug in `foreach`:
https://issues.dlang.org/show_bug.cgi?id=15413
2016-09-14 14:39 GMT+02:00 Jerry via Digitalmars-d <
digitalmars-d puremagic.com>:
I got a range which disables copy construction and I want to loop the
range within another loop using the same range.
So I thought I can mark the struct range with disable this(this) and then
use refRange to initialize the loop.
So with something like this:
void main()
{
auto valueRange = FooRange("123");
foreach(ch; refRange(&valueRange))
writeln(ch);
}
struct FooRange {
disable this();
disable this(this);
this(string str) {
this.str = str;
}
property bool empty() { return str.empty; }
property dchar front() { return str.front; }
void popFront() { str.popFront; }
private:
string str;
}
But I get compile time errors messages saying:
std/range/package.d(8155,23): Error: struct app.FooRange is not copyable
because it is annotated with disable
It feels strange that refRange ever want to copy.
Bug or feature?
Sep 14 2016
On 2016-09-14 14:39, Jerry wrote:
I got a range which disables copy construction and I want to loop the
range within another loop using the same range.
So I thought I can mark the struct range with disable this(this) and
then use refRange to initialize the loop.
So with something like this:
void main()
{
auto valueRange = FooRange("123");
foreach(ch; refRange(&valueRange))
writeln(ch);
}
struct FooRange {
disable this();
disable this(this);
this(string str) {
this.str = str;
}
property bool empty() { return str.empty; }
property dchar front() { return str.front; }
void popFront() { str.popFront; }
private:
string str;
}
But I get compile time errors messages saying:
std/range/package.d(8155,23): Error: struct app.FooRange is not copyable
because it is annotated with disable
It feels strange that refRange ever want to copy.
Bug or feature?
As a workaround you can take the address of the range and use
std.algorithm.each:
void main()
{
auto valueRange = FooRange("123");
(&valueRange).each!(ch => writeln(ch));
}
With a convenience function:
T* ptr(ref T t){ return &t; }
void main()
{
auto valueRange = FooRange("123");
valueRange.ptr.each!(ch => writeln(ch));
}
--
/Jacob Carlborg
Sep 15 2016