P2322 ranges::fold

[wg21bot]

P2322R0 ranges::fold (Barry Revzin)

[wg21bot]

P2322R1 ranges::fold (Barry Revzin)

[wg21bot]

P2322R2 ranges::fold (Barry Revzin)

[ben-craig]

2021-05-03 Library Evolution Telecon

P2322R2: ranges::fold

2021-05-03 Library Evolution Telecon Minutes

Chair: Ben Craig

Champion: Tim Song

Minute Taker: Inbal Levi

Start: 2021-05-03

POLL: fold with an initial value, and fold with no initial value and non-empty range should have different names (presumably fold and fold_first)

Strongly Favor	Weakly Favor	Neutral	Weakly Against	Strongly Against
6	6	3	2	1

Attendance: 27

# of Authors: 0

Author Position:

Outcome: Consensus in favor

SA: Most other languages don't use different names here. Very common to have one name and two forms

POLL: Rename fold_left to fold

Strongly Favor	Weakly Favor	Neutral	Weakly Against	Strongly Against
2	10	8	3	0

Attendance: 27

# of Authors: 0

Author Position:

Outcome: Very Weak Consensus. Mostly author's choice

POLL: Return the end iterator in addition to the result

Strongly Favor	Weakly Favor	Neutral	Weakly Against	Strongly Against
2	3	5	4	6

Attendance: 26

# of Authors: 0

Author Position:

Outcome: Weak consensus against

Suggested action: Others should provide data and rationale on where we have regretted not returning all the bits of information calculated by an algorithm.

POLL: Have a version of the fold algorithms that return the end iterator in addition to the result (as either an additional set of functions, or having some of the versions have different return values)

Strongly Favor	Weakly Favor	Neutral	Weakly Against	Strongly Against
4	9	3	3	1

Attendance: 24

# of Authors: 0

Author Position:

Outcome: Weak consensus in favor. Have a revision that addresses this issue. Would like motivation for or against in the next paper.

Example from a later reflector discussion where an end iterator would be useful:

fold_left(take(generator, 10), plus())

If you want to pick up from where take left off, you need fold_left to return an end iterator.