pass by const refererence about rcpp HOT 1 CLOSED

"It's complicated." You can do

> cppFunction("void twice(NumericVector x) { x = x + x; }")
> x <- c(2,4,8); twice(x); x
[1]  4  8 16
> 

which clearly changes x. The compiler slaps your fingers when you try to do this as cppFunction("void twice(const NumericVector x) { x = x + x; }") as it notices the assignment to the const declared x. But this only goes so far and if we want to trick it we can for example do

> cppFunction("void twice(const NumericVector x) { NumericVector y{x}; y = y + y; }")
> x <- c(2,4,8); twice(x); x
[1]  4  8 16
> 

where y as a shallow copy is actually a pointer reference and changes x.

So I think of the const as mostly for declaring intent and that is clearly the spirit of the intro example on page three.

from rcpp.