C#

N a v a n e e t h wrote:

class Vehicle

Here the "Car" instance is down casted into "Vehicle" instance. Is this performance costly ?

Or an approach with interfaces like the below one is better ?

Guffa wrote:

Why isn't the class abstract?

Guffa wrote:

You only have a use for the interface if you have a need to make a completely different implementation of the vehicle members for any class.

.method public hidebysig static class Vehicle CreateVehicle() cil managed
{
    .maxstack 8
    L_0000: newobj instance void Car::.ctor()
    L_0005: ret 
}

// C# code
public static Car ConvertToCar( Vehicle v )
{
    return (Car) v;
}
 
// IL code
 
.method public hidebysig static class Car ConvertToCar(class Vehicle v) cil managed
{
    .maxstack 8
    L_0000: ldarg.0 
    L_0001: castclass Car
    L_0006: ret 
}

// C# code
public static Car TryConvertToCar( Vehicle v )
{
    return v as Car;
}
 
public static bool IsCar( Vehicle v )
{
    return v is Car;
}
 
// IL code
.method public hidebysig static class Car TryConvertToCar(class Vehicle v) cil managed
{
    .maxstack 8
    L_0000: ldarg.0 
    L_0001: isinst Car
    L_0006: ret 
}
 
.method public hidebysig static bool IsCar(class Vehicle v) cil managed
{
    .maxstack 8
    L_0000: ldarg.0      // push v onto stack
    L_0001: isinst Car   // convert item on stack to a Car,
                         // or replace with null if it isn't one
    L_0006: ldnull       // push a null onto the stack
    L_0007: cgt.un       // Is the second item on the stack greater
                         // (unsigned) than the first? Replace top item
                         // with result
    L_0009: ret          // return top item on stack as result
}

public static bool IsCar( Vehicle v )
{
    Car c = v as Car;
    return c != null;
}

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