Re: subset of a POD
Hicham Mouline wrote:
I have functions that each take 1 parameter. This parameter is of type
struct S {
<arithmetic_or_bool_type_1> member_name_1;
<arithmetic_or_bool_type_n> member_name_n;
}; // n can be of order 10 or so
class C {
public:
return_type apply( const S& ) const;
};
Now I want to optimize the returned value.
"Optimize"?
I would optimize by fixing any subset of the n members fixed, ie none at
all, or just member 5, or members 4 and 8, or members 7,3 and n, or n-1
members of the {1....n} set.
How can I do this?
If your 'return_type' has to be the same *type*, there is no better
solution than to return an 'S', if the members that you don't want to
"return" are set to some "invalid" value. As an alternative you could
consider supplying another member to 'S', which would indicate the
"valid" or "active" members. You can have another (nested) struct in
'S' with bit fields:
struct S {
... // as you have now
struct {
unsigned use_1:1;
unsigned use_2:1;
...
unsigned use_n:1;
} which_members_to_use;
};
maybe
class C{
public:
pair<return_type, S> optimize(...) const; // returns the optimum S
that gives the best return value
What's "return_type" here? What does it mean for the return value to be
"the best"?
};
Some interface like this looks nice to me (as a user).
The question is how to pass the fixed members to optimize.
It is unclear what solution would be better since you've not explained
what problem you're trying to solve with this mechanism.
V
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