Check whether string value represents a type

[Timoses via Digitalmars-d-learn]

I'd love to check whether a string value is the name of a type at 
run-time.

E.g.:

string a = "int";
string b = "im no type";
assert( isStringType(a) );
assert( !isStringType(b) );

or

struct TestStruct
{
    int test;
}

string t = "TestStruct";
assert( isStringType(t) );


Is anything like this possible?

The goal is to identify whether a string represents a custom type 
within a package. I'm also trying to iterate over all modules 
within the package to get the struct name. However, that seems 
like a struggle...

Any ideas?..