is this even possible? newbie + mixin template + foreach (allMembers)

[Carlos Navarro via Digitalmars-d-learn]

QUESTION:

Obviously I'm no geting mixins/templates nor traits and I'm 
failing miserably to find/identify the right examples or 
documentation to help me tackle this thing. What is wrong in this 
code? is this pattern sintactically possible? what I'm getting 
wrong?

CONTEXT:
I'm a newbie trying to extend a struct using a mixin template 
like this one:

struct World {
        float    rotation;
        bool     active;
        mixin BuildStuff;
}

mixin template BuildStuff() {
        foreach(elem; __traits(allMembers, typeof(this))) {
                //pragma(msg, elem);
        }
} //full example here: https://run.dlang.io/is/OeXS4j

COMPILER OUTPUT:

2.067.1 to 2.071.2: Failure with output:
-----
onlineapp.d(18): Error: declaration expected, not 'foreach'
onlineapp.d(18): Error: declaration expected, not '__traits'
onlineapp.d(22): Error: template member expected
-----

2.072.2 to 2.075.1: Failure with output:
-----
onlineapp.d(18): Error: declaration expected, not 'foreach'
onlineapp.d(18): Error: declaration expected, not '__traits'
onlineapp.d(22): Error: matching '}' expected, not EOF
-----

Since      2.076.1: Segfault and no output