CODEWITHSUNDEEP
c#
MDiesel
MDiesel

Reputation: 2667

Type Cast Operator Precedence

I ran into a scenario today while implementing search functionality in my application that has left me puzzled. Check out this snippet:

public string GetFirstProductName(SortedList<string, object> itemsList) {
    for (int i = 0; i < itemsList.Values.Count; i++) {
        if (itemsList.Values[i] is Product)
           // Doesn't Compile:
           // return (Product)itemsList.Values[i].ProductName;

           // Does compile. Precedence for the "." higher than the cast?
           return ((Product)itemsList.Values[i]).ProductName;
        }
    }
}

So, what is the precedence for the cast? Is a cast an operator? What about the as keyword - is that an operator and what is its precedence?

Upvotes: 3

Views: 1891

Answers (4)

Shantanu Gupta
Shantanu Gupta

Reputation: 21108

It is not about precedence. Always value is converted

// Does compile. Precedence for the "." higher than the cast?
 return ((Product)itemsList.Values[i]).ProductName;

in your case value is being returned by itemsList.Values[i] which is being casted into Product. Then you are trying to access ProductName from it.

CAST is an Operator

Is/as works only on reference types

 return (itemsList.Values[i] as Product).ProductName;

READ MORE to understand difference between CAST and AS

Upvotes: 1

Lee
Lee

Reputation: 144206

x.y has a higher precedence than the cast:

7.3.1 Operator precedence and associativity

The following table summarizes all operators in order of precedence from highest to lowest:

Primary x.y f(x) a[x] x++ x-- new typeof default checked unchecked delegate

Unary + - ! ~ ++x --x (T)x

Upvotes: 4

LB2
LB2

Reputation: 4860

(Product)itemsList.Values[i].ProductName; means (Product)(itemsList.Values[i].ProductName); whereas second line you explicitly say to cast Values[i] and then do .ProductName;

Upvotes: 1

Simon Whitehead
Simon Whitehead

Reputation: 65077

Its quite simple really.

When you don't wrap the cast in brackets.. you're casting the entire expression:

return (Product)itemsList.Values[i].ProductName;
//              |______________________________|

You're essentially casting a string to a Product. Whereas:

return ((Product)itemsList.Values[i]).ProductName;
//     |____________________________|

Casts just that part, allowing the . to access the properties of a Product. Hopefully the bars help show you the difference more clearly.

Upvotes: 14

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