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Is there any downside to marking all C++ constructors explicit?

Asked 2011-04-18T13:14:43.717
19

A few times, when refactoring code, I have forgotten to add the explicit keyword when adding a parameter to a previously-parameterless constructor, or removing parameters from a previously multi-parameter constructor. To prevent this, I have gotten in the habit of marking every constructor explicit, no matter no many arguments it has. (Except, of course, those constructors for which I actually want implicit conversion.)

Is there any downside to this? Performance? Compile time?

c++ performance explicit-constructor
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15

It doesn't have any downsides. It will be future safe, because in C++0x multi-parameter constructors participate in initializations using multi-element initializer lists and can forbidden to be used in the cases where only implicit conversions apply using explicit.

So if you find out a give multi-parameter constructor does not logically represent the value of your class, I think it's good to make it explicit (example: I would set a container constructor (size_t size, T defaultValue) be explicit, while the constructor of pair, (T first, U second) be set non-explicit).

answered 2011-04-18T13:31:27.277

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