C# Language Specification

Explicit dynamic conversions

An explicit dynamic conversion exists from an expression of type dynamic to any type T. The conversion is dynamically bound (§7.2.2), which means that an explicit conversion will be sought at run-time from the run-time type of the expression to T. If no conversion is found, a run-time exception is thrown.

If dynamic binding of the conversion is not desired, the expression can be first converted to object, and then to the desired type.

Assume the following class is defined:

class C
{

int i;

public C(int i) { this.i = i; }

public static explicit operator C(string s)
{
return new C(int.Parse(s));
}
}

The following example illustrates explicit dynamic conversions:

object o = "1";

dynamic d = "2";

var c1 = (C)o; // Compiles, but explicit reference conversion fails

var c2 = (C)d; // Compiles and user defined conversion succeeds

The best conversion of o to C is found at compile-time to be an explicit reference conversion. This fails at run-time, because “1” is not in fact a C. The conversion of d to C however, as an explicit dynamic conversion, is suspended to run-time, where a user defined conversion from the run-time type of d – string – to C is found, and succeeds.

7.