Equality check for objects of classes with explicit constructor only

Question

Why can I not check two objects of classes with explicit constructor only for equality? The following code does not compile

struct Foo
{
    explicit Foo(int x) : x_(x) {}
    int x_;
};

int main()
{
    Foo(1) == Foo(1);
}

Do I have to declare operator == explicitly?

Answer 1

You need to overload the equality operator==:

struct Foo {
    explicit Foo(int x) : x_(x) {}
    int x_;
};

bool operator==(Foo const &lhs, Foo const& rhs) { return lhs.x_ == rhs.x_; }

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