Binary operator '<' cannot be applied to two 'Int?' operands

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一向
一向 2020-12-06 07:34

Good evening lovely community,
this is my first post, please have mercy, if I do something wrong.
I know there are some similar questions here, but I doesn\'t under

3条回答
  •  囚心锁ツ
    2020-12-06 08:10

    If you look at the declaration for Int's initializer that takes a String, you can see by the ? after init that it returns an optional:

    convenience init?(_ description: String)
    

    This means you have to unwrap it before you can do most things with it (== is an exception, since the Optional type has an overload for that operator).

    There are four main ways to unwrap your optionals:

    1: If let

    if let goalOne = Int(someString) {
        // do something with goalOne
    }
    

    2: Guard let

    guard let goalOne = Int(someString) else {
        // either return or throw an error
    }
    
    // do something with goalOne
    

    3: map and/or flatMap

    let someValue = Int(someString).map { goalOne in
        // do something with goalOne and return a value
    }
    

    4: Provide a default value

    let goalOne = Int(someString) ?? 0 // Or whatever the default value should be
    

    If you unwrap all your optionals, you'll be able to compare them as you expect.

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