`Contains`

Is one string contained in another? With Contains we search one string for a certain substring. We see if the string is found.

With other funcs like ContainsAny we search for characters. If any of a set of characters is found in the string, ContainsAny will return true.

First example

We have a string that contains "this is a test." The word "test" is found in the string. When we invoke Contains and search for "test," we receive true.

Argument 1 The first argument to Contains is a string. It is the string we are searching inside.

Argument 2 The second argument is the value we are searching for within the first argument.

package main

import (
    "fmt"
    "strings"
)

func main() {
    value1 := "test"
    value2 := "python"

    source := "this is a test"

    // This succeeds.
    // ... The substring is contained in the source string.
    if strings.Contains(source, value1) {
        fmt.Println(1)
    }

    // Contains returns false here.
    if !strings.Contains(source, value2) {
        fmt.Println(2)
    }
}1
2

`ContainsAny`

This method is different from Contains—it searches for characters. If any of the values in the second string argument to ContainsAny are found, it returns true.

Argument 1 The first argument to ContainsAny is the string we are searching for values within.

Argument 2 This is a set of values—just one has to be found for the method to return true.

package main

import (
    "fmt"
    "strings"
)

func main() {
    source := "12345"

    // See if 1, 3 or 5 are in the string.
    if strings.ContainsAny(source, "135") {
        fmt.Println("A")
    }

    // See if any of these 3 chars are in the string.
    if strings.ContainsAny(source, "543") {
        fmt.Println("B")
    }

    // The string does not contain a question mark.
    if !strings.ContainsAny(source, "?") {
        fmt.Println("C")
    }
}A
B
C

Contains is clearer than Index() when we just need to test existence. We can test against true and false, not the magical value -1 that Index() returns to mean "not found."