Guide to the Language

CHAPTER 23
Custom Conversions
This chapter covers how to define custom type conversions for an object. 
As seen in the following example, a class called MyNum is created with 
a single int field and a constructor. With a custom type conversion, it 
becomes possible to allow an int to be implicitly converted to an object of 
this class.
class MyNum
{
public int val;
public MyNum(int i) { val = i; }
}
 Implicit Conversion Methods
For this to work, an implicit conversion method needs to be added to 
the class. This method’s signature looks similar to that used for unary 
operator overloading. It must be declared as public static and includes 
the operator keyword. However, instead of an operator symbol the 
return type is specified, which is the target type for the conversion. The 
single parameter will hold the value that is to be converted. The implicit 
keyword is also included, which specifies that the method is used to 
perform implicit conversions.

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public static implicit operator MyNum(int a)
{
return new MyNum(a);
}
With this method in place, an int can be implicitly converted to a 
MyNum object.
MyNum a = 5; // implicit conversion
Another conversion method can be added that handles conversions in 
the opposite direction, from a MyNum object to an int.
public static implicit operator int(MyNum a)
{
return a.val;
}
 Explicit Conversion Methods
To prevent potentially unintended object type conversions by the compiler, 
the conversion method can be declared as explicit instead of implicit.
public static explicit operator int(MyNum a)
{
return a.val;
}
The explicit keyword means that the programmer has to specify an 
explicit cast in order to invoke the type conversion method. In particular, 
explicit conversion methods should be used if the result of the conversion leads 
to loss of information, or if the conversion method may throw exceptions.
MyNum a = 5;
int i = (int)a; // explicit conversion
Chapter 23 Custom Conversions

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© Mikael Olsson 2020 
M. Olsson, C# 8 Quick Syntax Reference, 
https://doi.org/10.1007/978-1-4842-5577-3_24