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package linq
import "reflect"
// Iterator is an alias for function to iterate over data.
type Iterator func() (item interface{}, ok bool)
// Query is the type returned from query functions.
// It can be iterated manually as shown in the example.
type Query struct {
Iterate func() Iterator
}
// KeyValue is a type that is used to iterate over a map
// (if query is created from a map). This type is also used by
// ToMap() method to output result of a query into a map.
type KeyValue struct {
Key interface{}
Value interface{}
}
// Iterable is an interface that has to be implemented by a
// custom collection in order to work with linq.
type Iterable interface {
Iterate() Iterator
}
// From initializes a linq query with passed slice, array or map
// as the source. String, channel or struct implementing Iterable
// interface can be used as an input. In this case From delegates it
// to FromString, FromChannel and FromIterable internally.
func From(source interface{}) Query {
src := reflect.ValueOf(source)
switch src.Kind() {
case reflect.Slice, reflect.Array:
len := src.Len()
return Query{
Iterate: func() Iterator {
index := 0
return func() (item interface{}, ok bool) {
ok = index < len
if ok {
item = src.Index(index).Interface()
index++
}
return
}
},
}
case reflect.Map:
len := src.Len()
return Query{
Iterate: func() Iterator {
index := 0
keys := src.MapKeys()
return func() (item interface{}, ok bool) {
ok = index < len
if ok {
key := keys[index]
item = KeyValue{
Key: key.Interface(),
Value: src.MapIndex(key).Interface(),
}
index++
}
return
}
},
}
case reflect.String:
return FromString(source.(string))
case reflect.Chan:
return FromChannel(source.(chan interface{}))
default:
return FromIterable(source.(Iterable))
}
}
// FromChannel initializes a linq query with passed channel,
// linq iterates over channel until it is closed.
func FromChannel(source <-chan interface{}) Query {
return Query{
Iterate: func() Iterator {
return func() (item interface{}, ok bool) {
item, ok = <-source
return
}
},
}
}
// FromString initializes a linq query with passed string,
// linq iterates over runes of string.
func FromString(source string) Query {
runes := []rune(source)
len := len(runes)
return Query{
Iterate: func() Iterator {
index := 0
return func() (item interface{}, ok bool) {
ok = index < len
if ok {
item = runes[index]
index++
}
return
}
},
}
}
// FromIterable initializes a linq query with custom collection passed.
// This collection has to implement Iterable interface, linq iterates over items,
// that has to implement Comparable interface or be basic types.
func FromIterable(source Iterable) Query {
return Query{
Iterate: source.Iterate,
}
}
// Range generates a sequence of integral numbers within a specified range.
func Range(start, count int) Query {
return Query{
Iterate: func() Iterator {
index := 0
current := start
return func() (item interface{}, ok bool) {
if index >= count {
return nil, false
}
item, ok = current, true
index++
current++
return
}
},
}
}
// Repeat generates a sequence that contains one repeated value.
func Repeat(value interface{}, count int) Query {
return Query{
Iterate: func() Iterator {
index := 0
return func() (item interface{}, ok bool) {
if index >= count {
return nil, false
}
item, ok = value, true
index++
return
}
},
}
}
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