On 03/22/08 10:24, Steven Watanabe wrote:
AMDG
Larry Evans wrote:
Could you post a test case with the before (only 1 expr with 3 args) [snip] arity and show how the 2 expr template method wouldn't work?
template<class Tag, class Args, int arity = Args::arity> struct expr3;
template<class Tag, class Args> struct expr3<Tag, Args, 2> { typename Args::arg0 arg0; typename Args::arg1 arg1; };
template<class Tag, class Args> struct expr2 { expr3<Tag, Args> args; };
struct test { int i; };
struct my_args { enum { arity = 2 }; typedef test arg0; typedef test arg1; };
struct my_tag {};
int main() { expr3<my_tag, my_args> x3 = { {1}, {1} }; expr2<my_tag, my_args> x2 = { {1}, {1} }; // error C2078: too many initializers }
To make x2 compile, add an extra {}, IOW x2 = { { {1}, {1} } } where the extran {} is for expr2::args. So, the cost of this extra indirection is 1 more curly braces in every expr initializer list?