Similarly, what would you gain by saying uint32_t const* x = my_var.get<uint32_t>();
To be frank: You gain the information that MyConcreteType::get<uint32_t> returns a uint32_t, which I otherwise couldn’t infer from the docs. Of course, I could assume it, based on the template parameter, but I don’t want to go around assuming a bunch of stuff in order to read docs.
Take an example like auto x = my_var.to_reduced_form(), it’s very clear that x is the “reduced form” of my_var, which could be meaningful in itself, but what type is it? I need to know that if I want to do anything with x. Can I do x += 1? If I do, will that modify my_var? Let’s say I want to make a vector of whatever to_reduced_form returns… and so on.
All these questions are very easily answered by MyConcreteTypex= my_var.to_reduced_form(). Now I immediately know that everything I can do with my_var, I can also do with x. This makes me happy, because I need to do less digging, and the code becomes clearer to read.
To answer you: no, x += 1 cannot mutate my_var, because it’s a copy. If you wanted something else you would say auto& or auto*.
And if the type of x is such that even a copy can mutate the original (e.g. maybe it’s a wrapper around an index with an overloaded operator+=() that mutates the original entry in the storage), you are probably working with a specialized system of some kind, since that breaks the semantics of the language, and hopefully you would know from context that you have such cases.
And yes, in such an environment I would see “never use auto for this wrapper type” as a valid additional strategy to help ensure code correctness.
But by and large my direct experience is that using auto “almost always”, as Herb Sutter puts it, is beneficial and doesn’t harm readability or understandability.
To be frank: You gain the information that
MyConcreteType::get<uint32_t>returns auint32_t, which I otherwise couldn’t infer from the docs. Of course, I could assume it, based on the template parameter, but I don’t want to go around assuming a bunch of stuff in order to read docs.Take an example like
auto x = my_var.to_reduced_form(), it’s very clear thatxis the “reduced form” ofmy_var, which could be meaningful in itself, but what type is it? I need to know that if I want to do anything withx. Can I dox += 1? If I do, will that modifymy_var? Let’s say I want to make avectorof whateverto_reduced_formreturns… and so on.All these questions are very easily answered by
MyConcreteType x = my_var.to_reduced_form(). Now I immediately know that everything I can do withmy_var, I can also do withx. This makes me happy, because I need to do less digging, and the code becomes clearer to read.To answer you: no,
x += 1cannot mutatemy_var, because it’s a copy. If you wanted something else you would sayauto&orauto*.And if the type of
xis such that even a copy can mutate the original (e.g. maybe it’s a wrapper around an index with an overloadedoperator+=()that mutates the original entry in the storage), you are probably working with a specialized system of some kind, since that breaks the semantics of the language, and hopefully you would know from context that you have such cases.And yes, in such an environment I would see “never use auto for this wrapper type” as a valid additional strategy to help ensure code correctness.
But by and large my direct experience is that using auto “almost always”, as Herb Sutter puts it, is beneficial and doesn’t harm readability or understandability.