如何在Go中优雅地迭代日期范围

Question

I need to iterate any specified dates range, say 2017-12-21 to 2018-01-05. What is the best way to implement that in Go?

output：
20171221
20171222
20171223
...
20180104
20180105

Answer 1

The Go Programming Language Specification

Function literals

A function literal represents an anonymous function.

FunctionLit = "func" Signature FunctionBody .

func(a, b int, z float64) bool { return a*b < int(z) }

A function literal can be assigned to a variable or invoked directly.

f := func(x, y int) int { return x + y }
func(ch chan int) { ch <- ACK }(replyChan)

Function literals are closures: they may refer to variables defined in a surrounding function. Those variables are then shared between the surrounding function and the function literal, and they survive as long as they are accessible.

---

In Go, encapsulate complexity in functions. Use a function literal as a closure.

For example,

package main

import (
    "fmt"
    "time"
)

// rangeDate returns a date range function over start date to end date inclusive.
// After the end of the range, the range function returns a zero date,
// date.IsZero() is true.
func rangeDate(start, end time.Time) func() time.Time {
    y, m, d := start.Date()
    start = time.Date(y, m, d, 0, 0, 0, 0, time.UTC)
    y, m, d = end.Date()
    end = time.Date(y, m, d, 0, 0, 0, 0, time.UTC)

    return func() time.Time {
        if start.After(end) {
            return time.Time{}
        }
        date := start
        start = start.AddDate(0, 0, 1)
        return date
    }
}

func main() {
    start := time.Now()
    end := start.AddDate(0, 0, 6)
    fmt.Println(start.Format("2006-01-02"), "-", end.Format("2006-01-02"))

    for rd := rangeDate(start, end); ; {
        date := rd()
        if date.IsZero() {
            break
        }
        fmt.Println(date.Format("2006-01-02"))
    }
}

Playground: https://play.golang.org/p/wmfQC9fEs1S

Output:

2018-06-22 - 2018-06-28
2018-06-22
2018-06-23
2018-06-24
2018-06-25
2018-06-26
2018-06-27
2018-06-28