Does the compiler reuse const variable declared inside method

Question

class foo
{
    string bar()
    {
        const string c = "dead beef";
        return c;
    }

    void Test()
    {
        string a = bar();
        string b = bar();
    }
}

are a and b different instance or are they pointing to the same memory address? (the == comparison would return true regardless they are the same instance or not so I can't really test it)

Strings are immutable, so you don't need to know or care. You can use Object.ReferenceEquals to find out though. — Blorgbeard
– Blorgbeard, Commented Jan 24, 2018 at 21:58
@Blorgbeard was wondering if im saving some tiny bit of resource for methods that will be called millions of times — Steve
– Steve, Commented Jan 24, 2018 at 22:00
@Steve Then measure how long it takes to run your method millions of times and see if changing the implementation changes the time. — Servy
– Servy, Commented Jan 24, 2018 at 22:01
If you'd like to see the difference local const variables have on the generated IL, take a look at a question I asked back in '09 - stackoverflow.com/questions/1707959/… — Richard Szalay
– Richard Szalay, Commented Jan 24, 2018 at 22:14
Imo, this would get inlined anyway, so doesn't matter. The call would never happen. — rokkerboci
– rokkerboci, Commented Jan 24, 2018 at 22:20

Richard Szalay · Accepted Answer · 2018-01-24 21:59:53Z

1

No, but it doesn't really matter for the majority of cases.

For structs (int, float, DateTime, etc) the value will placed on the stack so the memory reuse isn't relevant.

For strings, const doesn't do anything special but string constants themselves are interned so all matching constant string values will point to the same instance in memory.

answered Jan 24, 2018 at 21:59

Richard Szalay

85.1k19 gold badges186 silver badges242 bronze badges

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

2 Comments

Steve Over a year ago

interesting. that's why Object.ReferenceEquals(a, b) returns true or string but not int

Blorgbeard Over a year ago

Because ints are not objects, so they will boxed into (separate) object wrappers so they can be passed to ReferenceEquals.

Collectives™ on Stack Overflow

Does the compiler reuse const variable declared inside method

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related