issue48645b.go

     1  // run
     2  
     3  // Copyright 2021 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  type Iterator[T any] interface {
    10  	Iterate(fn func(T) bool)
    11  }
    12  
    13  type IteratorFunc[T any] func(fn func(T) bool)
    14  
    15  func (f IteratorFunc[T]) Iterate(fn func(T) bool) {
    16  	f(fn)
    17  }
    18  
    19  type Stream[T any] struct {
    20  	it Iterator[T]
    21  }
    22  
    23  func (s Stream[T]) Iterate(fn func(T) bool) {
    24  	if s.it == nil {
    25  		return
    26  	}
    27  	s.it.Iterate(fn)
    28  }
    29  
    30  func FromIterator[T any](it Iterator[T]) Stream[T] {
    31  	return Stream[T]{it: it}
    32  }
    33  
    34  func (s Stream[T]) DropWhile(fn func(T) bool) Stream[T] {
    35  	return Pipe[T, T](s, func(t T) (T, bool) {
    36  		return t, true
    37  	})
    38  }
    39  
    40  func Pipe[T, R any](s Stream[T], op func(d T) (R, bool)) Stream[R] {
    41  	it := func(fn func(R) bool) {
    42  		// XXX Not getting the closure right when converting to interface.
    43  		// s.it.Iterate(func(t T) bool {
    44  		// 	r, ok := op(t)
    45  		// 	if !ok {
    46  		// 		return true
    47  		// 	}
    48  
    49  		// 	return fn(r)
    50  		// })
    51  	}
    52  
    53  	return FromIterator[R](IteratorFunc[R](it))
    54  }
    55  
    56  func Reduce[T, U any](s Stream[T], identity U, acc func(U, T) U) (r U) {
    57  	r = identity
    58  	s.Iterate(func(t T) bool {
    59  		r = acc(r, t)
    60  		return true
    61  	})
    62  
    63  	return r
    64  }
    65  
    66  type myIterator struct {
    67  }
    68  
    69  func (myIterator) Iterate(fn func(int) bool) {
    70  }
    71  
    72  func main() {
    73  	s := Stream[int]{}
    74  	s.it = myIterator{}
    75  	s = s.DropWhile(func(i int) bool {
    76  		return false
    77  	})
    78  	Reduce(s, nil, func(acc []int, e int) []int {
    79  		return append(acc, e)
    80  	})
    81  }
    82
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