QHash<float,int> and `qHash(const float&)' is ambiguous error

[jpn]

From QHash docs:

Here's a list of the C++ and Qt types that can serve as keys in a QHash: any integer type (char, unsigned long, etc.), any pointer type, QChar, QString, and QByteArray. For all of these, the <QHash> header defines a qHash() function that computes an adequate hash value. If you want to use other types as the key, make sure that you provide operator==() and a qHash() implementation.