8e8d570571
Proposes a set of core features for declaring and implementing generic
variadic
functions.
A "pack expansion" is a syntactic unit beginning with `...`, which is a
kind of
compile-time loop over sequences called "packs". Packs are initialized
and
referred to using "pack bindings", which are marked with the `each`
keyword at
the point of declaration and the point of use.
The syntax and behavior of a pack expansion depends on its context, and
in some
cases by a keyword following the `...`:
- In a tuple literal expression (such as a function call argument list),
`...`
iteratively evaluates its operand expression, and treats the values as
successive elements of the tuple.
- `...and` and `...or` iteratively evaluate a boolean expression,
combining
the values using `and` and `or`, and ending the loop early if the
underlying
operator short-circuits.
- In a statement context, `...` iteratively executes a statement.
- In a tuple literal pattern (such as a function parameter list), `...`
iteratively matches the elements of the scrutinee tuple. In conjunction
with
pack bindings, this enables functions to take an arbitrary number of
arguments.
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Co-authored-by: josh11b <josh11b@users.noreply.github.com>
Co-authored-by: Richard Smith <richard@metafoo.co.uk>
Co-authored-by: josh11b <15258583+josh11b@users.noreply.github.com>
Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
Co-authored-by: Carbon Infra Bot <carbon-external-infra@google.com>
Principles
Some language goals will have widely-applicable, high-impact, and sometimes non-obvious corollaries. We collect concrete language design principles in this directory as a way to document and clarify these. Principles clarify, but do not supersede, goals and priorities. Principles should be used as a tool in making decisions, and to clarify to contributors how decisions are expected to be made.
A key difference between a principle and the design of a language feature is that a principle should inform multiple designs, whereas a feature's design is typically more focused on achieving a specific goal or set of goals. The principle can help achieve consistency across those multiple designs.
Note that these principles seek to establish both the approaches the project wants to pursue, as well as those we want to exclude.