To replace a substring within a string in Rust 1.55, you can use the replace method. This method takes two arguments as strings: the substring to be replaced and the replacement substring. Here's an example:
let mut my_string = String::from("Hello, world!");
let new_string = my_string.replace("world", "Rust");
println!("{}", new_string);
In the above example, we create a String variable called my_string with the value "Hello, world!". We then use the replace method to replace the substring "world" with "Rust", and store the result in a new String variable called new_string. Finally, we print the value of the new string, which should be "Hello, Rust!".
Here's another example, where we replace all occurrences of a substring within a string:
let mut my_string = String::from("The quick brown fox jumps over the lazy dog.");
let new_string = my_string.replace("the", "a");
println!("{}", new_string);
In this example, we replace all occurrences of the substring "the" with "a". The resulting string should be "The quick brown fox jumps over a lazy dog.".
Using the replace method is an easy and efficient way to replace substrings within a larger string in Rust.