P1751 Numeric Type Families

[wg21bot]

P1751R0 Numeric Type Families (John McFarlane)

[johnmcfarlane]

Reviewed at the same time as P0554.

[brycelelbach]

Cologne 2019-07 LEWGI Minutes

P0554R1 Compositional Numeric Types: Design Feedback

P1751R0 Numeric Type Families: Design Feedback

Champion: John McFarlane

Minute Taker: Billy O'Neal

Start Overview: 07-16 13:42

Start Review: 14:03

Composition design - Unary adaptor types that compose vs an Nary type with multiple properties.

// Unary adaptor types that compose.
template <typename Rep> struct a_integer;
template <typename Rep> struct b_integer;
template <typename Rep> struct c_integer;

vs

// Nary type with ordered properties.
struct a_tag {};
struct b_tag {};
struct c_tag {};

template <typename... Properties>
struct integer;

POLL: We want unary adaptor types that compose instead of exploring a type with nary ordered properties.

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
4	7	2	2	1

A: Would love to see other designs explored.

That has consensus.

Attendance: 18

Explore a compositional helper.

POLL: We should promise more committee time to pursuing new arithmetic types in the standard library that satisfy the use cases described in P0554, knowing that our time is scarce and this will leave less time for other work.

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
6	7	2	1	0

Attendance: 16

This has strong consensus.

elastic_integer<20, int> // Status quo.
elastic_integer<70, wide_integer<31>> // Status quo, works through traits.
elastic_integer<20, int_family>

POLL: We are okay with representing families of arithmetic types with a single, unique member of that family and traits (e.g. int for signed integers, unsigned for unsigned integers).

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
0	2	5	7	2

Attendance: 18

End: 15:35

CONSENSUS: Bring a revision of P0554R1, with the guidance below, to LEWGI for further design feedback.

• Consider merging the various other integer type papers targeting the Numeric TS into P0554.
• Produce draft wording.
• Explore an alternative design to numeric type families which does not rely on using a single unique member of each family and traits to represent the family.