Extract an element from a structure?

[Caike Du]

Dear all,
I write a function with the return of a structure. How can I extract the elements of the structure in another function? See the example below. Function aaa returns a struct my. I use function aaa in function bbb, and put its return in q. Then I want to extract the element a of structure q and store it in ccc. When I run the code, Stata reports errors as follows. Is there any way to extract an element from a structure?



------------------------------------------
mata mata clear
mata

struct mypoint {
real vector a
real vector b
}
end

mata
function aaa(real vector a, real vector b)
{
struct mypoint scalar my
my.a=b
my.b=a
return(my)
}
end

mata
function bbb(real vector a, real vector b)

{
q=aaa(a,b)
ccc=q.a
return(ccc)
}

end


--------------------------------------

: function bbb(real vector a, real vector b)
>
> {
> q=aaa(a,b)
> ccc=q.a
type mismatch: exp.exp: transmorphic found where struct expected
r(3000);

: return(ccc)
'return' found where almost anything else expected
r(3000);

: }
expression invalid
r(3000);

[Joseph Coveney]

Try putting

struct mypoint scalar q

just before the line

q = aaa(a, b)

.

Actually, I recommend explicitly declaring all of your variables (and function return datatypes) as a habit. Use

mata set matastrict on

to help with that.

[Caike Du]

Try putting

struct mypoint scalar q

just before the line

q = aaa(a, b)

.

Actually, I recommend explicitly declaring all of your variables (and function return datatypes) as a habit. Use

mata set matastrict on

to help with that.

It works. Thanks very much!