How does let x where x.hasSuffix(“pepper”) work

问题:

In the code block below, I am having trouble understanding let x where x.hasSuffix("pepper").

let vegetable = "red pepper"  switch vegetable {     case "celery":         let vegetableComment = "Add some raisins and make ants on a log."     case "cucumber", "watercress":         let vegetableComment = "That would make a good tea sandwhich"     case let x where x.hasSuffix("pepper"):         let vegetableComment = "Is it a spicy \(x)"     default:         let vegetableComment = "Everything tastes good in soup." } 

Console output

vegetableComment: Is it a spicy red pepper

It seems like the following logic is happening.

x = vegetable if (x's suffix == 'pepper')      run case 

Can someone explain this better for me?

回答1:

vegetable is an implicit String. It's the same as you would write:

var vegetable: String = "red pepper" 

hasSuffix is declared as func hasSuffix(suffix: String) -> Bool an therefore returns a Bool. The where keyword specifies additional requirements, and can only be used in switch statements.
Because all of this is suffused, the vegetable variable is assigned to x (let x).

You can read more about the where and switch here.

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