Programming C#, Second Edition

Reflection Emit

So far we’ve seen reflection used for three purposes: viewing metadata, type discovery, and dynamic invocation. You might use these techniques when building tools (such as a development environment) or when processing scripts. The most powerful use of reflection, however, is with reflection emit.

Reflection emit supports the dynamic creation of new types at runtime. You can define an assembly to run dynamically or to save itself to disk, and you can define modules and new types with methods that you can then invoke.

Tip

The use of dynamic invocation and reflection emit should be considered an advanced topic. Most developers will never have need to use reflection emit. This demonstration is based on an example provided at the Microsoft Author’s Summit, Fall 2000.

To understand the power of reflection emit, you must first consider a slightly more complicated example of dynamic invocation.

Problems can have general solutions that are relatively slow and specific solutions that are fast. To keep things manageably simple, consider a DoSum( ) method, which provides the sum of a string of integers from 1...n, where n will be supplied by the user.

Thus, DoSum(3) is equal to 1+2+3, or 6. DoSum(10) is 55. Writing this in C# is very simple:

public int DoSum1(int n)
{
    int result = 0;
    for(int i = 1;i <= n; i++)
    {
        result += i;
    }
    return result;
}

The method simply loops, adding the requisite number. If you pass in 3, the method adds 1 + 2 + 3 and returns an answer of 6.

With large ...