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SOLVED: Cannot assign to property because the value being assigned is a let constant

Forums > SwiftUI
@lordmooch  HWS+

In the code snippet below I am trying to assign a value from the array activityDays to a variable and then use that variable on the following line.

However, the line that assigns a value to name won't compile, because activityTypeName is a let constant. I don't understand why that matters?

    init(activityDays: Binding<[ActivityDay]>, action: Binding<ActivityListActions>, tags: [TagSelected]) {

        _activityDays = activityDays
        _action = action
        self.tags = tags

        var activityTypes: [ActivityTypeSelected] = []

        for activity in activityDays {

            var name = activity.activityTypeName // Won't compile because activityTypeName is a let constant - but why should that matter?
            activityTypes.append(ActivityTypeSelected(activityTypeName: name, isSelected: false))

        }

    }

Is this something to do with the parameter being a Binding? I can't even do

print(activity.activityTypeName)

in the loop - it gives me the same error.

2      

@roosterboy  HWS+

Please give us some more code. Without knowing anything about ActivityDay and ActivityTypeSelected, we can't copy/paste your code to reproduce the issue and figure out a solution. (We don't need ActivityListAction or TagSelected because those aren't involved in the problem.)

2      

@microenh  

I think what you need to do is access the wrapped value of the @Binding, you do that by putting an underscore in front of it.

var name = _activity.activityTypeName

2      

@roosterboy  HWS+

An underscore accesses the property wrapper itself, not the wrapped value.

That's why you do this when assigning a Binding parameter to a property:

_activityDays = activityDays

But yeah, accessing the wrapped value solves the error:

for activity in activityDays.wrappedValue {

    var name = activity.activityTypeName
    activityTypes.append(ActivityTypeSelected(activityTypeName: name, isSelected: false))

}

2      

@microenh  

Well, at least I was half-right 😀

2      

@lordmooch  HWS+

Oh. My. Goodness.

Thank you very much!

2      

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