insert a string into another string at a specific index in rust

You can insert a string into another string at a specific index in Rust by first obtaining a mutable reference to the target string, and then using the insert() method provided by the standard library's String type.

Here is an example code block:

main.rs
fn main() {
    let mut target = String::from("Hello, world!");
    let to_insert = "beautiful ";

    // Insert the to_insert string at index 6
    target.insert_str(6, to_insert);

    println!("{}", target);
}
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In this example, we first create a mutable string variable target with the value "Hello, world!". We also create another string to_insert with the value "beautiful ", which we want to insert into target at index 6.

We then use the insert_str() method provided by String, passing in the index 6 and the to_insert string. This method moves the existing characters at the specified index to the right and inserts the new characters in their place.

After inserting the string, we print the new value of target, which will be "Hello, beautiful world!".

Note that the insert() and insert_str() methods take the index as the first argument and the string to insert as the second argument. If you want to insert a single character, you can use the insert() method instead and pass a single char as the second argument.