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 | Posted by Tomoya Tanjo |  Permalink Reply |
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Tomoya Tanjo 
| http://d.puremagic.com/issues/show_bug.cgi?id=10570
Summary: Example of `how` function for AutoImplement should
work for non-abstract class
Product: D
Version: D2
Platform: All
OS/Version: All
Status: NEW
Severity: normal
Priority: P2
Component: Phobos
AssignedTo: nobody@puremagic.com
ReportedBy: ttanjo@gmail.com
--- Comment #0 from Tomoya Tanjo <ttanjo@gmail.com> 2013-07-08 04:52:47 PDT ---
The generateLogger function is an example of `how` function for
std.typecons.AutoImplement and
is defined in the comment of AutoImplement.
It works for interface and abstract class, but it does not work for the
non-abstract class with a method
that returns non-string (e.g. void).
The reason is that it only consider the return type of itself, not the return
type of method to be overridden.
The following code reproduce the problem. It should be compiled succesfully but it does not:
----
// It is coped from the comment of std.typecons.AutoImplement.
// Prints log messages for each call to overridden functions.
string generateLogger(C, alias fun)() @property
{
enum qname = C.stringof ~ "." ~ __traits(identifier, fun);
string stmt;
stmt ~= q{ struct Importer { import std.stdio; } };
stmt ~= `Importer.writeln("Log: ` ~ qname ~ `(", args, ")");`;
static if (!__traits(isAbstractFunction, fun))
{
static if (is(typeof(return) == void)) // typeof(return) is always
string!
stmt ~= q{ parent(args); };
else
stmt ~= q{
auto r = parent(args);
Importer.writeln("--> ", r);
return r;
};
}
return stmt;
}
// A class to be overridden
class Foo{
void bar(int a) { }
}
// Logger template
template Logger(Base)
{
import std.typecons;
alias Logger = AutoImplement!(Base, generateLogger, isThrowable);
}
// to avoid overriding toHash (it is nothrow but writeln is not nothrow)
template isThrowable(alias fun)
{
import std.traits;
enum isThrowable = !functionAttributes!fun ||
(functionAttributes!fun & !FunctionAttribute.nothrow_);
}
void main()
{
auto foo = new Logger!Foo();
foo.bar(13);
}
----
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