Refer to the same parameter multiple times in a fmt.Sprintf format string

问题

I have this function:

func getTableCreationCommands(v string) string {
    return `
        CREATE TABLE share_` + v + ` PARTITION OF share FOR VALUES IN (` + v + `);
        CREATE TABLE nearby_` + v + ` PARTITION OF nearby FOR VALUES IN (` + v + `);
    `
}

It's a little wonky... is there a way to format the string using fmt.Sprintf?

Something like this:

func getTableCreationCommands(v string) string {
    return fmt.Sprintf(`
        CREATE TABLE share_%v PARTITION OF share FOR VALUES IN (%v);
        CREATE TABLE nearby_%v PARTITION OF nearby FOR VALUES IN (%v);
    `, v, v, v, v)
}

but without the need to pass v 4 times?

回答1:

Package fmt
import "fmt" 
Explicit argument indexes:

In Printf, Sprintf, and Fprintf, the default behavior is for each formatting verb to format successive arguments passed in the call. However, the notation [n] immediately before the verb indicates that the nth one-indexed argument is to be formatted instead.

You can pass the variable v once. For example,

package main

import "fmt"

func getTableCreationCommands(v string) string {
    return fmt.Sprintf(`
        CREATE TABLE share_%[1]v PARTITION OF share FOR VALUES IN (%[1]v);
        CREATE TABLE nearby_%[1]v PARTITION OF nearby FOR VALUES IN (%[1]v);
    `, v)
}

func main() {
    fmt.Println(getTableCreationCommands(("X")))
}

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

Output:

CREATE TABLE share_X PARTITION OF share FOR VALUES IN (X);
CREATE TABLE nearby_X PARTITION OF nearby FOR VALUES IN (X);

来源：https://stackoverflow.com/questions/53026706/refer-to-the-same-parameter-multiple-times-in-a-fmt-sprintf-format-string

标签

string-formatting