Re: [Boost-users] [boost][array] Multi-dimensional initialization

Michael Marcin wrote:

At least under MSVC 8 I can do:

boost::array< boost::array, 4 > foo = { -1,1, 0,0, 1,-1, 2,-2 }; or

int foo[4][2] = { {-1,1}, {0,0}, {1,-1}, {2,-2} };

or

boost::array foo[4] = { {-1,1}, {0,0}, {1,-1}, {2,-2} };

but not

boost::array< boost::array, 4 > foo = { {-1,1}, {0,0}, {1,-1}, {2,-2} };

just wondering why this is the case.

To initialize a boost::array "by the book" you need double braces: boost::array foo = {{ 1, 2 }}; because a boost::array is essentially struct array { int data[2]; }; and, according to the initializer rules, the outer braces are for the array struct, and the inner braces correspond to the data[] array. In most cases you can drop the outer braces. In your last example, however, dropping them creates an ambiguity, and you need: boost::array< boost::array, 4 > foo = {{ {-1,1}, {0,0}, {1,-1}, {2,-2} }};