I was reading Explicitly defaulted and deleted special member functions, and saw that in order to call only the function f with double and avoid an implicit conversion, one could write this (from the same page):

struct OnlyDouble
{
    void f(double d);
    template<class T> void f(T) = delete;
};

Is there a reason why one would write the code above instead of this code below?

struct OnlyDouble
{
    explicit void f(double d);
};

Any difference, or is there some extra behavior that I don't know of?

CodePudding user response：

Two things:

1. explicit is not valid for functions so the explicit void f(double); doesn't compile.
2. explicit doesn't prevent implicit conversions of arguments.

That is, even if the comparison were between:

struct OnlyDouble
{
    OnlyDouble(double d);
    template<class T> OnlyDouble(T) = delete;
};

and

struct OnlyDouble
{
    explicit OnlyDouble(double d);
};

You're right that both would error on:

OnlyDouble od = 42;

but following is ill-formed for the first and well-formed for the second:

OnlyDouble od(42);