[Rcpp-devel] Delayed usage of auxiliary memory in RcppArmadillo

[Simon Zehnder]

Dear Rcpp::Devels and Rcpp::Users,

I am temporarily experiencing with a delayed assignment of auxiliary memory in RcppArmadillo:

Declare a matrix from which you know you may need it

arma::mat maybeM;

(In C++ a declaration makes only known the type and name but allocates no storage yet).

Now you check a condition and if it is true, you will need the matrix, so you initialize it 

if(mycondition) {
	maybeM = arma::mat(aux_mem*, n_rows, n_cols, copy_aux_mem = false, strict = true) 
}

(for simplicity I only printed here the default constructor for using auxiliary memory; please assume that all values are presented)

The resulting matrix maybeM does not use the auxiliary memory. I tried to access in some way the 'mem' member in the Armadillo class, but this member is constant and can not be
manipulated after first construction. A primer declaration and later initialization is a very common pattern in C++, but it seems not be possible in case of reusing memory. 

I conclude, that a delayed assignment of auxiliary memory is not possible.


Best

Simon
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