Comments on: Using C++11 auto and decltype

By: Dmitri

Dmitri — Wed, 15 Aug 2012 16:39:04 +0000

In addition to what was said in this article, I think the great benefit of keyword `auto` is its use follow the DRY principle. It also allows to capture the intention of coder more accurately. Consider:

int f() { return 42; }

int x = f(); // In this line, what we really want is a variable x of type whatever f() returns, which we have to write explicitly as int, violating DRY

auto y = f(); // This does not violate DRY, and matches the intention of having variable x of type whatever f() returns

That said, all these auto and decltype keywords make it more mandatory to have a good IDE with type induction. While previously you could use notepad and Search to find the type of a given variable, now that process becomes more convoluted. Instead, your IDE should be able to tell you what the type of any variable is right away.

By: Boris Kolpackov

Boris Kolpackov — Tue, 14 Aug 2012 19:24:24 +0000

Jesse, only if auto is not used to form a reference the top-level const-qualifier is stripped. I know this is a lot of "if-this-then-that" special cases. That's why I like the idea of mentally re-writing a statement with auto into a function template. Consider:



template <typename T>

void g1 (T x);

 

template <typename T>

void g2 (T& x);

 

g1 (f ()); // T is int (not const int), x is int

g2 (f ()); // T is const int, x is const int&

By: Jesse

Jesse — Tue, 14 Aug 2012 18:30:13 +0000

You first say this:

const int& f3 ();
auto a3 = f3 (); // a1 is int

Then you say that

const int& f ();
auto& x = f (); // auto -> const int, x is const int&

Wouldn’t this imply that:
auto& x = f (); // auto -> int, x is int&