How to pass variables to string mixins?

[Victor Porton]

I want to create a string mixin based on a supplementary variable 
(name2 below):

Let we have something like:

mixin template X(string name) {
   immutable string name2 = '_' ~ name;
   mixin("struct " ~ name2 ~ "{ int i; }");
}

But it would create variable name2 inside X, which should not be 
created. How to solve this problem?