# Building a chain of responsibility with delegates

Imagine that you have to write a function that verifies if there is a license available for a given clientID. Suppose that there are a couple of possibilities to find an available license. Your code would probably look like the following

```
// This code verifies if the client with the given clientID is licensed
// returns the licenseID or 0 if no license is available
public Int32 IsLicensed(Int32 clientID)
{
int result = 0;
// verify if there is already a license 'assigned' to the client
result = IsAssigned(clientID);
if (result == 0)
{
// find a dedicated license (license that is bound to the given client)
result = IsDedicated(clientID);
if (result == 0)
{
// find a nondedicated license (license that can be used by any client)
result = IsNonDedicated(clientID);
}
}
return result;
}
```

It’s obvious that this structures becomes more complex as the number of possible ways to get a license grows. If you look a while at the structure you’ll notice a pattern: each function (IsAssigned, IsDedicated, IsNonDedicted) verifies if there is a license availble. If the function didn’t find a license the next function is performed. If you translate this to OO you would end up with something similar to the following

```
// this methods tries to find an available license for the given clientID
// returns the licenseID or 0 if no license was found
delegate Int32 FindLicenseMethod(Int32 clientID);
public class LicenseFinder
{
private FindLicenseMethod method;
private LicenseFinder next;
public LicenseFinder(FindLicenseMethod, method, LicenseFinder next)
{
this.method = method;
this.next = next;
}
// property for the next licensefinder in the chain
public Next
{
get { return next; }
set { next = val; }
}
public Int32 GetLicense(Int32 clientID)
{
Int32 result = method(clientID);
if (result == 0 && Next != null)
{
result = Next.GetLicense(clientID);
}
return result;
}
public Int32 IsLicensed(Int32 clientID)
{
LicenseFinder f = new LicenseFinder(
new FindLicenseMethod(IsAssigned), new LicenseFinder(
new FindLicenseMethod(IsDedicated), new LicenseFinder(
new FindLicenseMethod(IsNonDedicated), null))));
return f.GetLicense(clientID);
}
}
```