To me, a = struct(...) and a(1) = struct(...) should both work equally well when a is empty.
When a is an empty structure array, Yes. When a is an empty double, I agree with matlab it should not, since you're changing the type of the variable.
Note that you'll have the same problem with other types that do not convert to double:
a = []; %create an empty double
a(end+1) = struct('x', 0) %not allowed since you're trying to put a structure into an array of double
a(end+1) = {'x'} %also not allowed to put a cell into an array of double
a(end+1) = datetime %also not allowed with classes. Cannot convert datetime to double
The workaround is to pass an empty structure (with the correct fields) instead of an empty double:
a = struct('x', {}); %create empty structure array
a(end+1) = struct('x', 1); %no error
So call your function with:
a = addto(struct('field1', {}), 1)
the first time round. Or indeed, test for empty double in the function.
