Lazy var initialization error "Cannot use mutating getter on immutable value"

Question

I tried two ways of initializing a lazy var, one works, the other gets a compiler error.

OK: var maxDiscount = MaxDiscount(); maxDiscount.maxDiscountPercent
ERROR: MaxDiscount().maxDiscountPercent If maxDiscountPercent was a stored property rather than a lazy var both usages would work.

Simplified example:

struct MaxDiscount {
        lazy var maxDiscountPercent: Int = {
        print("Lazy var maxDiscountPercent initialized")
        return 256
    }()
    
}
// initializes lazy var without an error

var maxDiscount = MaxDiscount()
print("Max percent discount: ", maxDiscount.maxDiscountPercent)

// initializes lazy var with error:
// "Cannot use mutating getter on immutable value: function call returns immutable value"

var maxDiscountPercent = MaxDiscount().maxDiscountPercent
print("Max percent discount: ", maxDiscountPercent)

It's not clear to me why one usage is mutable and the other immutable.

Frédéric LOYER · Accepted Answer · 2023-04-24 20:50:41Z

3

When you write var maxDiscount, you declare a variable (mutable). You would have a constant (immutable) with let maxDiscount = MaxDiscount().

Now with var maxDiscountPercent = MaxDiscount().maxDiscountPercent, MaxDiscount() is an anonymous constant and you can't do everything on it.

Try let maxDiscount = MaxDiscount() and you will get the same type of error and an invitation to change let by var.

edited Apr 24, 2023 at 20:50

answered Apr 24, 2023 at 20:40

Frédéric LOYER

1,0647 silver badges10 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Lazy var initialization error "Cannot use mutating getter on immutable value"

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related