[Qt-interest] qhash - user defined key type

[Yifei Li]

Thank you for the reply.

I did provide an implementation like yours. The implementation was omitted to make the minimal example look concise :)

Anything else you can think of?

Yifei
----- Original Message -----
From: "Jonas Gehring" <jonas.gehring at boolsoft.org>
To: qt-interest at trolltech.com
Sent: Thursday, August 20, 2009 4:08:09 PM GMT -05:00 US/Canada Eastern
Subject: Re: [Qt-interest] qhash - user defined key type

Hi,

You need to provide an implementation of qHash(const Test::Foo&), like

	inline uint qHash(const Foo& f) {
		return qHash(f.id());
	}

This one is using qHash(int), as provided by Qt itself.


Regards,
Jonas


On Thursday 20 August 2009 21:43:00 Yifei Li wrote:
> Here is the problem I'm having with QHash right now ( Below is a minimal
> example that will reproduce my problem)
>
> /** Header file from some third-party library */
>
> namespace Test {
> class Foo{
> public:
>    Foo(id);
>    int id() const { return m_id; }
> private:
>    int m_id;
> };
> }
>
> /** My header file */
>
> using namespace Test;
>
> class Bar{
> public:
>    void init()
>    {
>        Foo f(1);
>        indicators[f] = false;
>    }
> private:
>    QHash<Foo, bool>  indicators;
> };
>
> //  overload operators so that Foo can be used as a key type
> inline bool operator==(const Foo& f1, const Foo&f2)
> inline uint qHash(const Foo& f);
>
> /** main.cpp */
> int main
> {
>     Bar b;
>     b.init();
>     return 0;
> }
>
> /** Failed to compile the above code */
> ERROR: no matching function for call to ‘qHash(const Test::Foo&)’
>
> What should I do to get rid of the error? thanks
>
>
> Yifei
>
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> Qt-interest at trolltech.com
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