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// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build goexperiment.rangefunc
// Package iter provides basic definitions and operations
// related to iteration in Go.
//
// This package is experimental and can only be imported
// when building with GOEXPERIMENT=rangefunc.
package iter
import (
"internal/race"
"unsafe"
_ "unsafe"
) // for linkname
// Seq is an iterator over sequences of individual values.
// When called as seq(yield), seq calls yield(v) for each value v in the sequence,
// stopping early if yield returns false.
type Seq[V any] func(yield func(V) bool)
// Seq2 is an iterator over sequences of pairs of values, most commonly key-value pairs.
// When called as seq(yield), seq calls yield(k, v) for each pair (k, v) in the sequence,
// stopping early if yield returns false.
type Seq2[K, V any] func(yield func(K, V) bool)
type coro struct{}
//go:linkname newcoro runtime.newcoro
func newcoro(func(*coro)) *coro
//go:linkname coroswitch runtime.coroswitch
func coroswitch(*coro)
// Pull converts the “push-style” iterator sequence seq
// into a “pull-style” iterator accessed by the two functions
// next and stop.
//
// Next returns the next value in the sequence
// and a boolean indicating whether the value is valid.
// When the sequence is over, next returns the zero V and false.
// It is valid to call next after reaching the end of the sequence
// or after calling stop. These calls will continue
// to return the zero V and false.
//
// Stop ends the iteration. It must be called when the caller is
// no longer interested in next values and next has not yet
// signaled that the sequence is over (with a false boolean return).
// It is valid to call stop multiple times and when next has
// already returned false.
//
// It is an error to call next or stop from multiple goroutines
// simultaneously.
func Pull[V any](seq Seq[V]) (next func() (V, bool), stop func()) {
var (
v V
ok bool
done bool
racer int
)
c := newcoro(func(c *coro) {
race.Acquire(unsafe.Pointer(&racer))
yield := func(v1 V) bool {
if done {
return false
}
v, ok = v1, true
race.Release(unsafe.Pointer(&racer))
coroswitch(c)
race.Acquire(unsafe.Pointer(&racer))
return !done
}
seq(yield)
var v0 V
v, ok = v0, false
done = true
race.Release(unsafe.Pointer(&racer))
})
next = func() (v1 V, ok1 bool) {
race.Write(unsafe.Pointer(&racer)) // detect races
if done {
return
}
race.Release(unsafe.Pointer(&racer))
coroswitch(c)
race.Acquire(unsafe.Pointer(&racer))
return v, ok
}
stop = func() {
race.Write(unsafe.Pointer(&racer)) // detect races
if !done {
done = true
race.Release(unsafe.Pointer(&racer))
coroswitch(c)
race.Acquire(unsafe.Pointer(&racer))
}
}
return next, stop
}
// Pull2 converts the “push-style” iterator sequence seq
// into a “pull-style” iterator accessed by the two functions
// next and stop.
//
// Next returns the next pair in the sequence
// and a boolean indicating whether the pair is valid.
// When the sequence is over, next returns a pair of zero values and false.
// It is valid to call next after reaching the end of the sequence
// or after calling stop. These calls will continue
// to return a pair of zero values and false.
//
// Stop ends the iteration. It must be called when the caller is
// no longer interested in next values and next has not yet
// signaled that the sequence is over (with a false boolean return).
// It is valid to call stop multiple times and when next has
// already returned false.
//
// It is an error to call next or stop from multiple goroutines
// simultaneously.
func Pull2[K, V any](seq Seq2[K, V]) (next func() (K, V, bool), stop func()) {
var (
k K
v V
ok bool
done bool
)
c := newcoro(func(c *coro) {
yield := func(k1 K, v1 V) bool {
if done {
return false
}
k, v, ok = k1, v1, true
coroswitch(c)
return !done
}
seq(yield)
var k0 K
var v0 V
k, v, ok = k0, v0, false
done = true
})
next = func() (k1 K, v1 V, ok1 bool) {
race.Write(unsafe.Pointer(&c)) // detect races
if done {
return
}
coroswitch(c)
return k, v, ok
}
stop = func() {
race.Write(unsafe.Pointer(&c)) // detect races
if !done {
done = true
coroswitch(c)
}
}
return next, stop
}
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