http://d.puremagic.com/issues/show_bug.cgi?id=9528
Summary: std.array.appender can't append elements with const
members
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: Phobos
AssignedTo: [email protected]
ReportedBy: [email protected]
--- Comment #0 from [email protected] 2013-02-17 17:37:08 PST ---
Code:
------------------------------------------
import std.array;
E[] fastCopy(E)(E[] src) {
auto app = appender!(const(E)[])();
foreach (i, e; src)
app.put(e);
return app.data;
}
E[] slowCopy(E)(E[] src) {
E[] result;
foreach (i, e; src)
result ~= e;
return result;
}
void main() {
class C {}
struct S { const(C) c; }
S[] s = [ S(new C) ];
//auto t = fastCopy(s); // Does not compile
auto t = slowCopy(s);
}
------------------------------------------
If fastCopy is used in place of slowCopy, dmd git head gives:
------------------------------------------
/usr/src/d/phobos/std/array.d(2256): Error: cannot modify struct
(cast(S*)(*this._data).arr)[len] S with immutable members
test.d(6): Error: template instance
std.array.Appender!(const(S)[]).Appender.put!(S) error instantiating
test.d(22): instantiated from here: fastCopy!(S)
test.d(7): Error: cannot implicitly convert expression (app.data()) of type
const(S)[] to S[]
test.d(22): Error: template instance test.fastCopy!(S) error instantiating
------------------------------------------
Is there any workaround for this? What I'm trying to accomplish is to copy an
array of elements with const fields, but selectively skip elements based on
some predicate (so straight .dup is out of the question). But using =~ is slow
because of continual resizing/reallocation.
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