[Swig-user] Treat Returned Reference as Value

[Jake]

I feel like I must just be missing this in the documentation somewhere, but
when a function returns a reference SWIG treats that like a pointer by
default. How do we tell it to treat it as a value (i.e. make a copy and
wrap that)?

For example:

struct Example {
int& get(int x, int y);
};

I want the int copied and not as a SWIG_int_p.

-Jake Cobb

[schullq]

Do you include "typemaps.i" ?

If not, include it, and take a look a it ([swig folder]/Lib/[your target
language]/typemaps.i]), you should get your answer here.



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[William S Fulton]

Post by Jake
I feel like I must just be missing this in the documentation somewhere,
but when a function returns a reference SWIG treats that like a pointer by
default. How do we tell it to treat it as a value (i.e. make a copy and
wrap that)?
struct Example {
int& get(int x, int y);
};
I want the int copied and not as a SWIG_int_p.

const int& is marshalled by value in Java/C#. You can thus simply use these
typemaps. There are various ways, but I suggest using %apply:

%apply const int& { int& } // Everywhere (including input parameters and
on function return)

%apply const int& { int& Example::get} // Just for this function's return

Post by Jake
Do you include "typemaps.i" ?
If not, include it, and take a look a it ([swig folder]/Lib/[your target
language]/typemaps.i]), you should get your answer here.
typemaps.i is for changing the way a function's parameters are marshalled,

so not of any use for a function's return. You'll notice there are no 'out'
typemaps in this file which is what generates the C code for returning
types from a function.

William

[Jake]

Post by William S Fulton
%apply const int& { int& Example::get} // Just for this function's return

I think this is what I'm looking for since std::vector wrapping provided by
std_vector.i
has a non-const return on operator[]. Thanks.

-Jake Cobb