Method overload with object parameters

Question

if I define two methods:

void foo(object a);

void foo(string a);

and then call foo("test") can I be sure that the second method is invoked?

Answer 1

Try it for yourself, just put a breakpoint in, whatever happens the first time always will. Another interesting one to try would be this:

object obj = "test";
foo(obj);

Answer 2

well, I do not want to test it :) I tried to find compiler rules on this case but failed.

I want to be sure that there is a compiler rule and would be happy to see a reference to documentation. I do not want to hope that it works like the test showed

Answer 3

Here is the Method Overload Resolution from the C# Language Specification.

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I always try to Keep it Sharp & simple.

Answer 4

Welcome to C# spec - 14.4.2 Overload resolution

Compiler looks for the "better function member" which is:

"...Given an argument list A with a sequence of argument types {A1, A2, …, AN} and two applicable function members MP and MQ with parameter types {P1, P2, …, PN} and {Q1, Q2, …, QN, MP}, after expansion and type argument substitution,is defined to be a better function member than MQ if
• for each argument, the implicit conversion from AX to PX is not worse than the implicit conversion from AX to QX, and
• for at least one argument, the conversion from AX to PX is better than the conversion from AX to QX..."

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codevanced.net

Answer 5

ok. so foo(string) will be invoked on foo("test") as well as on foo(a) where a is of type object with value "test".

Answer 6

No. Given that you have

void foo(string a);
void foo(object a);

and call foo with object parameter (that contains string), then the overload that takes object will be invoked - the second one from the above - because "foo(object)" is a better function member for an object parameter.

Moreover if you'd have a custom class with implicit conversion defined

public class MyString
{
    public string Data {get;set;};
    public static implicit operator string(MyString o)
    {
        return o.Data;
    }
}

then you could have used it in your foo invocations - foo(string) would be used. In this case, both conversions are valid - MyString can be converted to object and it can be converted to string with implicit conversion we provided - but custom string conversion is consitered to be a better one.

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codevanced.net

Answer 7

got you. my mistake