Must ranges have value semantics?

Chris Wright via Digitalmars-d-learn digitalmars-d-learn at
Tue Dec 15 09:36:52 PST 2015

I noticed that some methods in Phobos will have very different behavior 
with forward ranges that have reference semantics and those that have 
value semantics.


auto range = getSomeRange();
auto count = range.walkLength;
foreach (element; range) { writeln(element); }

If getSomeRange returns a forward range that is a reference type with 
no .length property, walkLength will exhaust the range. The iteration 
after that will never enter the loop body.

However, if getSomeRange returns a range with value semantics with 
no .length property, then iteration is still possible.

I haven't found documentation about how ranges are intended to be used in 
D written by people who maintain Phobos. Is it normal and expected that I 
should have to call .save everywhere, manually? Was there discussion on 
whether this should be the case or a published document containing the 
reasoning behind the decision?

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