Question

For signal and slot of below type

signals:
    void textChanged(const QString &);

public slots:
    void setText(const QString & text)

the type of argument of textChanged and setText seems to work invarable of const and &. Does the constant and reference qualification make any difference compared to just using QString ?

QObject::connect(a,SIGNAL(textChanged(QString)),b,SLOT(setText(QString)));
QObject::connect(a,SIGNAL(textChanged(const QString &)),b,SLOT(setText(const QString &)));

EDIT:
I did not notice the output window showing error messages when there is incompatible type being used in SIGNAL or SLOT. I thought the signal slot mechanism is capable of detecting argument type error at compile time.

Answer 1

Qt checks a normalized signature, meaning

Normalization reduces whitespace to a
minimum, moves ‘const’ to the front
where appropriate, removes ‘const’
from value types and replaces const
references with values.