[ConceptGCC]|
[ConceptGCC] |
ConceptGCC :Re: Need some help -- can't find the error in this code. |
From: Tom Honermann (tom.honermann_at_[hidden])
Date: 2007-09-17 15:32:52
Hi Daniel,
I'm not 100% sure about this answer, but here goes...
When defining a concept, identifiers that do not explicity quantify type
attributes (such as 'const' or '&') are defaulted to 'const type&'. So,
in your 'Function<F>' concept, the use of 'source_type' and
'target_type' on line 19 will become:
const target_type& operator()(const source_type& x);
As far as I know, there is no way to enforce "copy by value" arguments
when defining a concept - but there also seems to be no reason to do so
since a 'const type&' will generally suffice - and provide better
flexibility for defining concept_maps.
Regardless, the use of 'const type&' should be ok for your test case.
I don't really understand the error message for line 53. However, I
wonder if this is just a poor message for another error. In your 'test'
function, the 'f' parameter is specified as "copy by value", but the
'Function' concept does not specify that the type is copy constructible,
so this use is not valid (I think). There are a couple of ways of
fixing this:
1. Add another requires clause to 'test' that 'F' be CopyConstructible
2. Change 'test' to accept it's F parameter as a reference.
Tom.
Daniel Lincke wrote:
>Hi ConceptGCC-users,
>
>I tried ConceptGCC and my first programm don't work. Here is the code:
>
>+++++++++++++++++++++++++++++++++++++++++++++++++
>#ifdef __GXX_CONCEPTS__
>#include <concepts>
>#endif
>
>#include <stdlib.h>
>#include <stdio.h>
>#include <iostream>
>
>using namespace std;
>
>#ifdef __GXX_CONCEPTS__
>concept Function<class F> {
>typename source_type;
>typename target_type;
>
>target_type operator() (source_type x); // LINE 19
>!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>};
>#endif
>
>class Test_Function1 {
>public:
>typedef int source_type;
>typedef int target_type;
>
>int operator() (int t) {
>return (t*2);
>}
>};
>
>
>#ifdef __GXX_CONCEPTS__
>concept_map Function<Test_Function1> {
>typedef Test_Function1::source_type source_type;
>typedef Test_Function1::target_type target_type;
>
>target_type operator() (source_type x) {
>//return Test_Function1::operator() (x);
>Test_Function1 f;
>return f(x);
>}
>}
>#endif
>
>template<class F>
>#ifdef __GXX_CONCEPTS__
>requires Function<F>
>#endif
>void test (F f) {
>for (int i=0; i<10; ++i)
>{cerr << i << " -> " << f(i) << endl;} // LINE 53
>!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
>}
>
>int main (int argc, char *argv[]) {
>
>}
>
>++++++++++++++++++++++++++++++++++++++++++++++++++++++
>
>ConceptGCC reports the following error:
>
>/opt/conceptgcc-4.3/bin/conceptg++ -c -o main.o main.cpp
>main.cpp: In function ‘void test(F)’:
>main.cpp:53: error: invalid initialization of reference of type ‘const
>Function<F>::source_type&’ from expression of type ‘F’
>main.cpp:19: error: in passing argument 1 of ‘Function<F>::target_type
>Function<F>::operator()(const Function<F>::source_type&)’
>make: *** [main.o] Fehler 1
>
>
>lines 19 and 53 are marked in the listing above. I don't understand the
>error: in passing argument 1 of ‘Function<F>::target_type
>Function<F>::operator()(const Function<F>::source_type&)’
>message, as there is no such operator in the concept Function, at least
>not with an const reference as input parameter.
>
>Greets and Thanks for reducing my confusion ;)
>Daniel
>_______________________________________________
>ConceptGCC mailing list
>ConceptGCC_at_[hidden]
>http://www.osl.iu.edu/mailman/listinfo.cgi/conceptgcc
>
>
-- Oracle Email Signature Logo Tom Honermann | Senior Principal Software Engineer | 503.276.2354 Oracle PeopleTools Development 1211 SW 5th Ave, Suite 9080, Portland, OR 97204
