Speed wise it almost certainly doesn’t matter – any decent C++ compiler is just going to pass a single int. The important point is readability – which will make your code more obvious to the reader? If it’s obvious that these enums are really just ints then I would pass them by value, as if … Read more
According to this answer, Qt just replaces const references with copies. EDIT: Apparently not always the case… I just did a basic test program with one thread, and the reference was passed correctly. Its const-ness remained intact, as well. Anyways, yes, you do need to be wary of the variable going out of scope, plus … Read more
Actually, this is the precise reason why perfect forwarding was introduced. Rewrite the constructor as template <typename L, typename O> LinearClassifier(L && loss, O && optimizer) : _loss(std::forward<L>(loss)) , _optimizer(std::forward<O>(optimizer)) {} But it will probably be much simpler to do what Ilya Popov suggests in his answer. To be honest, I usually do it this … Read more
1. Is getA1() implementation correct ? I feel it is incorrect as it is returning address of local variable or temporary. The only version of getAx() that is correct in your program is getA3(). Both of the others have undefined behaviour no matter how you use them later. 2. Which of the statements in main … Read more
Welcome to const and reference collapsing. When you have const T&, the reference gets applied to T, and so does the const. You call g like g<int&>(n); so you have specified that T is a int&. When we apply a reference to an lvalue reference, the two references collapse to a single one, so int& … Read more
There is no difference unless you write something weird like (v1 += v2) = v3; In the first case, the assignment will be to a temporary, and the overall effect will be v1 += v2. In the second case, the assignment will be to v1, so the overall effect will be v1 = v3. In … Read more
Only local const references prolong the lifespan. The standard specifies such behavior in ยง8.5.3/5, [dcl.init.ref], the section on initializers of reference declarations. The reference in your example is bound to the constructor’s argument n, and becomes invalid when the object n is bound to goes out of scope. The lifetime extension is not transitive through … Read more