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 | Posted by Jonathan M Davis |  Permalink Reply |
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Jonathan M Davis 
| http://d.puremagic.com/issues/show_bug.cgi?id=8367
Summary: std.range.chain's template constraint is inadequate
Product: D
Version: unspecified
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: Phobos
AssignedTo: nobody@puremagic.com
ReportedBy: jmdavisProg@gmx.com
--- Comment #0 from Jonathan M Davis <jmdavisProg@gmx.com> 2012-07-10 00:18:01 PDT ---
This code fails to compile
import std.algorithm;
import std.range;
struct Foo {}
void main()
{
auto f = Foo();
auto foos = [f];
auto foo = foos.map!(x => "foo");
auto bar = foo.chain("bar");
}
giving this string of errors:
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(1934): Error: cannot
have parameter of type void
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(1934): Error:
variable std.range.chain!(Result,string).chain.Result.fixRef.val variables
cannot be of type void
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(1936): Error: cannot
return non-void from void function
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(1996): Error:
function std.range.chain!(Result,string).chain.Result.fixRef (void val) is not
callable using argument types (string)
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(1996): Error: cannot
implicitly convert expression (this.source._field_field_0.front()) of type
string to void
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(1996): Error:
function std.range.chain!(Result,string).chain.Result.fixRef (void val) is not
callable using argument types (dchar)
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(1996): Error: cannot
implicitly convert expression (front(this.source._field_field_1)) of type dchar
to void
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2026): Error: cannot
return non-void from void function
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2026): Error: cannot
return non-void from void function
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2039): Error:
function std.range.chain!(Result,string).chain.Result.fixRef (void val) is not
callable using argument types (dchar)
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2039): Error: cannot
implicitly convert expression (back(this.source._field_field_1)) of type dchar
to void
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2039): Error:
function std.range.chain!(Result,string).chain.Result.fixRef (void val) is not
callable using argument types (string)
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2039): Error: cannot
implicitly convert expression (this.source._field_field_0.back()) of type
string to void
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2061): Error: cannot
return non-void from void function
/home/jmdavis/dmd2/linux/bin/../../src/phobos/std/range.d(2061): Error: cannot
return non-void from void function
q.d(11): Error: template instance std.range.chain!(Result,string) error
instantiating
The code shouldn't compile. It's trying to chain an array of strings and a string. The types don't match. However, the error is _horrible_. Since the given arguments won't compile with chain, they shouldn't pass chain's template constraint (either that or chain must have a series of static asserts which output informative error messages for types which won't work with chain). But obviously, chain's template constraint is passing with arguments which fail to compile with chain, and that needs to be fixed.
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