[MPL?] generating functions for all fields in a struct
Given a struct like struct X { int a; char b; float c; } and some function-'template' f is it possible to 'generate' - preferably by means of templates, MPL or something of the kind - variations of some function f for each of X's fields? E.g. I'd like to have functions like int getA() { return a; } char getB() { return b; } float getC() { return c; } ... (The functions I have in mind are more complex, obviously, but the idea is to generate one such function for all the fields of X.) I would like to avoid writing a macro call or something per field, as I would like the code to work (after recompiling it) even if the definition of X is changed and some fields are added. So, is there some generic 'iterator' over the fields of a struct? Thank you and best regards Christoph
on Thu Mar 08 2007, Christoph Duelli <duelli-AT-melosgmbh.de> wrote:
Given a struct like struct X { int a; char b; float c; } and some function-'template' f
is it possible to 'generate' - preferably by means of templates, MPL or something of the kind - variations of some function f for each of X's fields?
E.g. I'd like to have functions like int getA() { return a; } char getB() { return b; } float getC() { return c; } ...
(The functions I have in mind are more complex, obviously, but the idea is to generate one such function for all the fields of X.) I would like to avoid writing a macro call or something per field, as I would like the code to work (after recompiling it) even if the definition of X is changed and some fields are added. So, is there some generic 'iterator' over the fields of a struct?
Nope. You might consider using Boost.Fusion and using a tuple instead of a struct. You won't be able to generate a family of overloaded functions at namespace scope, but you will be able to generate a family of overloaded (static) member functions. -- Dave Abrahams Boost Consulting www.boost-consulting.com
David Abrahams wrote:
on Thu Mar 08 2007, Christoph Duelli <duelli-AT-melosgmbh.de> wrote:
Given a struct like struct X { int a; char b; float c; } and some function-'template' f
is it possible to 'generate' - preferably by means of templates, MPL or something of the kind - variations of some function f for each of X's fields?
E.g. I'd like to have functions like int getA() { return a; } char getB() { return b; } float getC() { return c; } ...
(The functions I have in mind are more complex, obviously, but the idea is to generate one such function for all the fields of X.) I would like to avoid writing a macro call or something per field, as I would like the code to work (after recompiling it) even if the definition of X is changed and some fields are added. So, is there some generic 'iterator' over the fields of a struct?
Nope.
You might consider using Boost.Fusion and using a tuple instead of a struct. You won't be able to generate a family of overloaded functions at namespace scope, but you will be able to generate a family of overloaded (static) member functions.
You can also map your struct(s) to a fusion tuple. The mapping can be a simple "tie". Example: fusion::vector<int&,char&,float&> map_struct(X& x) { return fusion::tie(x.a, x.b, x.c); } Then you can refer to x.a through at_c<1>, x.b through at_c<2> and x.c through at_c<3>. If you want your fields to be non-positional (i.e. a field named "a" can always be referred to somehow regardless of its position in the struct), then you can use fusion::map and map various keyword types to each of the fields. Example: struct a_; struct b_; struct c_; fusion::result_of::map_tie< a_, int&, b_, char&, c_, float& > map_struct(X& x) { return fusion::map_tie<a_type, b_type, c_type>(x.a, x.b, x.c); } Then you can refer to x.a through at_key<a_>, x.b through at_key<b_> and x.c through at_key<c_>. Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net
On 3/9/07, Joel de Guzman <joel@boost-consulting.com> wrote:
map_struct(X& x) { return fusion::map_tie<a_type, b_type, c_type>(x.a, x.b, x.c);
a_type? return fusion::map_tie<a_, b_, c_>(x.a, x.b, x.c); ?
}
Tony
Gottlob Frege wrote:
On 3/9/07, Joel de Guzman <joel@boost-consulting.com> wrote:
map_struct(X& x) { return fusion::map_tie<a_type, b_type, c_type>(x.a, x.b, x.c);
a_type? return fusion::map_tie<a_, b_, c_>(x.a, x.b, x.c); ?
Yep. Sorry. Thanks for the correction! Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net
participants (4)
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Christoph Duelli -
David Abrahams -
Gottlob Frege -
Joel de Guzman