Catching errors

When an error is thrown from a function, we need to catch it in the code that called it; this is done using the do-catch block. We use the try keyword, within the do-catch block, to identify the places in the code that may throw an error. The do-catch block with a try statement has the following syntax:

do {
    try [Some function that throws]
    [Code if no error was thrown]
} catch [pattern] {
    [Code if function threw error]
}

If an error is thrown, it is propagated out until it is handled by a catch clause. The catch clause consists of the catch keyword, followed by a pattern to match the error against. If the error matches the pattern, the code within the catch block is executed.

Let's look at how to use the do-catch block by calling both the getPlayerByNumber() and addPlayer() methods of the BaseballTeam structure. Let's look at the getPlayerByNumber() method first, since it only throws one error condition:

do {
    let player =...