Huangzj
72 lines
2.6 KiB
Go
72 lines
2.6 KiB
Go
package linq
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// Select projects each element of a collection into a new form.
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// Returns a query with the result of invoking the transform function
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// on each element of original source.
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//
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// This projection method requires the transform function, selector,
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// to produce one value for each value in the source collection.
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// If selector returns a value that is itself a collection,
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// it is up to the consumer to traverse the subcollections manually.
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// In such a situation, it might be better for your query to return a single
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// coalesced collection of values. To achieve this, use the SelectMany method
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// instead of Select. Although SelectMany works similarly to Select,
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// it differs in that the transform function returns a collection
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// that is then expanded by SelectMany before it is returned.
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func (q Query) Select(selector func(interface{}) interface{}) Query {
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return Query{
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Iterate: func() Iterator {
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next := q.Iterate()
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return func() (item interface{}, ok bool) {
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var it interface{}
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it, ok = next()
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if ok {
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item = selector(it)
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}
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return
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}
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},
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}
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}
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// SelectIndexed projects each element of a collection into a new form
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// by incorporating the element's index. Returns a query with the result
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// of invoking the transform function on each element of original source.
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//
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// The first argument to selector represents the zero-based index of that element
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// in the source collection. This can be useful if the elements are in a known order
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// and you want to do something with an element at a particular index,
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// for example. It can also be useful if you want to retrieve the index of one
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// or more elements. The second argument to selector represents the element to process.
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//
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// This projection method requires the transform function, selector,
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// to produce one value for each value in the source collection.
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// If selector returns a value that is itself a collection,
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// it is up to the consumer to traverse the subcollections manually.
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// In such a situation, it might be better for your query to return a single
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// coalesced collection of values. To achieve this, use the SelectMany method
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// instead of Select. Although SelectMany works similarly to Select,
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// it differs in that the transform function returns a collection
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// that is then expanded by SelectMany before it is returned.
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func (q Query) SelectIndexed(selector func(int, interface{}) interface{}) Query {
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return Query{
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Iterate: func() Iterator {
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next := q.Iterate()
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index := 0
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return func() (item interface{}, ok bool) {
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var it interface{}
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it, ok = next()
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if ok {
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item = selector(index, it)
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index++
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}
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return
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}
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},
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}
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}
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