QTextBrowser and friend function

[probine]

I have a class that creates a window and a text browser. The text browser is displayed in the window.

I want other classes to be able to print something in that text browser, therefore I have decided to declare it "friend". With this idea, any class can just "include" the window class an be able to print something.

The window class has this function:

friend void displayMessage(QString message){
     textBrowser->append(message);
}

friend void displayMessage(QString message){
     textBrowser->append(message);
}

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Note that textBrowser is public in the window class.

How can I make something like this work ?