Class value members & references

[agnus]

Hello, I am still fighting with C++ references! Lets say we have this:

class Foo {
 
    public:
    Foo(Bar& b);
 
    private:
    Bar m_bar;
};
 
Foo::Foo(Bar& b) : m_bar(b) {}

class Foo {

    public:
    Foo(Bar& b);

    private:
    Bar m_bar;
};

Foo::Foo(Bar& b) : m_bar(b) {}

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1. Should the constructor better have the parameter as value instead of reference?
2. Since I am using the constructor initialization list, would there be a performance difference?
3. Would there be a semantic difference? e.g., to the caller of new Foo

Thank you again