std::make_pair vs C++11 uniform initializer

c++ c++11 uniform-initialization
rubenvb picture rubenvb · Mar 13, 2011 · Viewed 11k times · Source

Is there a drawback to using the latter? Is std::make_pair more versatile/compatible or are they truly interchangeable?

Thanks!

Answer

Johannes Schaub - litb picture Johannes Schaub - litb · Mar 13, 2011

How are they related? Using an initializer list constructor doesn't work for a pair, because a pair is heterogeneously typed, while an initializer list constructor uses an initializer_list<T>, which is only usable to retrieve an homogeneously typed initializer list.

(Looking into the spec, it should really be called "initializer-list constructor", instead of "initializer list constructor". Do you really mean to refer to the first? If not, what do you refer to?).

If you just refer to initialize a std::pair<> using an initializer list against using std::make_pair and using auto, I think both are fine. 

auto p = std::make_pair(a, b);
std::pair<A, B> p{a, b};

If you have already the types A and B and can use them for the pair, then the initializer list is a good way to use. If you haven't, then make_pair might be a good thing. If you have types A and B, but aren't sure whether they are already transformed properly (i.e they should not be array or function types, and you probably also want them to be non-reference types), then it might be easier to use std::make_pair, which will properly decay the type of the expressions.

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