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c++constructorc++11explicit-constructor
Klaim
Klaim

Reputation: 69752

Explicit on N-ary constructors?

In this presentation: http://qtconference.kdab.com/sites/default/files/slides/mutz-dd-speed-up-your-qt-5-programs-using-c++11.pdf

The author suggests that N-ary constructors benefit from the C++11 version of explicit keyword.

What changed in C++11 that makes this keyword useful if you have more than one constructor parameter?

Upvotes: 10

Views: 737

Answers (1)

Joseph Mansfield
Joseph Mansfield

Reputation: 110698

In C++11, if you have a non-explicit constructor for a class A that has multiple parameters (here I use A::A(std::string, int, std::string) as an example), you can initialize an argument of that type with brace initialization:

void foo(A a);
foo({"the", 3, "parameters"});

Similarly, you can do the same with return values:

A bar() {
  return {"the", 3, "parameters"};
}

If the constructor is, however, explicit, these will not compile. Hence, the explicit keyword now has importance for all constructors, rather than just conversion constructors.

Upvotes: 16

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