On Saturday, 22 December 2012 at 08:55:35 UTC, bearophile wrote:
I sometimes write code like:auto data = File("data.txt") .byLine() .map!(r => r.strip().dup)() .filter!(r => !r.empty)() .array();To help writing/improving/debugging such code maybe it's useful to create a pass() range in Phobos. It's like a "identity range" that just passes its inputs to its output, but also runs a given lambda to the items that pass through it (the lambda receives a const item, to avoid modifications of the data passing through the chain):auto data = File("data.txt") .byLine() .pass(r => writeln("A: ", r)) .map!(r => r.strip().dup)() .pass(r => writeln("B: ", r)) .filter!(r => !r.empty)() .array();This usage of pass() allows to introduce debug prints inside very long chains of such iterables, with no need to break them apart and assign the parts to temporary variables just to see what's going on in that chain.But it's not hard to do it with a not pure map: .map!((r){ writeln("B: ", r); return r; })() Or even with an evil comma operator: .map!(r => (writeln("B: ", r), r))() So I don't know how much useful that pass() is. Bye, bearophile
Bug reporting aside, it can be useful in the sense of *doing* something to each element, as opposed to "call a function and re-assign to original element".
This would be especially true for say: Mutating functions that return void, or just plain calling member functions.
I think it's a legit request. If anything, *map* could be re-implemented in terms of *call*.
