Using "if let" with logical "or" operator

Question

I'm trying to write the following block of code in a single if let line:

 if let amount = datasource?.incrementForCount?(count) {

        count += amount
    }

    else if let amount = datasource?.fixedIncrement {
        count += amount
    }

when I try something like:

 if let amount = datasource?.incrementForCount?(count) ||  let amount = datasource?.fixedIncrement {

        count += amount
    }

I got a compile time error.

I don't think that where clause is possible for this case.

Is it possible to combine the two if let statements into a single ORed one?

Avt · Accepted Answer · 2015-12-13 11:55:48Z

61

Try to use ?? operator:

if let amount = datasource?.incrementForCount?(count) ?? datasource?.fixedIncrement 
{
    count += amount
}

is it possible to combine the 2 if let statements into a single ORed one ?

It is possible to have several let statements like

if let a = optionalA, b = optionalB { ... }

And all of them should return non-nil value to pass.

But if you also want to use a logical condition it:

Could be only the one
Should be placed on the first place, before any let statements

edited Dec 13, 2015 at 11:55

answered Dec 13, 2015 at 11:03

Avt

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3 Comments

JAHelia Over a year ago

is there a cleaner solution to use when there are further ORed conditions instead of nesting ?? operator statetments ?

Avt Over a year ago

@JAHelia No. You can have only one logical condition in if statement (not where) and it should be placed on the first place, before any let statements.

Mojo66 Over a year ago

I don't know when it was changed but Swift 5.4 requires the following syntax: if let a = optionalA, let b = optionalB { ... }

TheBaj · Accepted Answer · 2017-02-13 13:02:11Z

19

No, you can't OR two if-let statements, or even an if-let statement with a non if-let condition, because that would completely defeat the purpose of the if-let statement. if-let ensures that you can only enter the body of the statement if the optional could be successfully unwrapped into the variable.

let str:String? = nil
if let s = str || true {
  //s is nil, yet you're still in the if-let body
}

In the above example you would still enter the optional body even if s were nil, in which case you would still have to check whether sis nil or not inside the body, rendering the first if-let check pointless.

answered Feb 13, 2017 at 13:02

TheBaj

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2 Comments

Nicholas Over a year ago

Disagreed. There are instances where you need to use an optional when a condition is met, but if that condition's not met you don't need to use that optional. Example: you need an ID to initialize a controller, but depending on what the server gives, you might use the default value. This is when it's best to combine if let and || since the init code is the same. This is convenient: if let id = model.id || model.usesDefaultValue { /*init code here once*/ } This is not: if let id = model.id { /*init here*/ } else if model.usesDefaultValue { /*same init - code repetition*/ }

MechEthan Over a year ago

This is correct -- to clarify, let's say Swift tried to allow that statement. When if let s = str evaluates to true, that means that s is not an optional, but when evaluates to false, that means s would need to be an optional. s cannot both be an optional and a non-optional at the same time, so it can't compile.

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