...

qtab.d

struct Section {
    
    this(QTabFile file, string tag) {
        ...
    }
    
    /// Allows to iterate over section lines with foreach.
    int opApply(int delegate(string) call_line) {
        ...
    }

    string[string] dict() @property {
        ... /* lazily initialized */
    }
}

class QTabFile {

    this(string filename) { ... }

    /// just syntax sugar
    Section opIndex(string tag) { 
        return Section(this, tag);
    }

    void close() { ... }
}  

auto f = new QTabFile(...);
scope(exit) f.close();
foreach(line; f["Genotype Symbol"]) {
    ...
}