Re: [Boost-users] [range] filtered dereferences underlying range elements twice

High cost sometime if filtered always store dereferenced-value. I think memoized adaptor was better to external store design. or add stored_filtered adaptor. 2011/6/1 Akira Takahashi :

Nate, follow is filtered + transformed adaptor's internal behavior.

[filtered] increment iterator behavior: while (!pred(*it)) ++it;

dereference iterator behavior: *it;

[transformed] increment iterator behavior: ++it;

dereference iterator behavior: f(*it);

[filtered | transformed] increment iterator behavior: while (!pred(*it)) ++it;

dereference iterator behavior: f(*it);

[transformed | filtered] increment iterator behavior: while (!pred(f(*it))) ++it;

dereference iterator behavior: f(*it);

oven::memoized is call once function by stored calculation.

2011/6/1 Nathan Ridge :

...

Thanks Akira, it is good to know that there is a workaround.

But I was wondering, is it necessary in the first place for filtered to dereference the underlying range elements twice?

Thanks, Nate.

...

======================== Akira Takahashi mailto:faithandbrave@gmail.com blog:http://d.hatena.ne.jp/faith_and_brave/