In D, all semantic analysis of a template waits until instantiation time. This is because D is designed so that the syntax parsing does not need a symbol table.

In C++, I solved this problem by simply matching { } in the template body, and accumulating a list of tokens within the { }. Then, when instantiated, the template parameter values were known, and the template syntax could then be semantically analyzed. It was simple and effective.

But I was informed that C++ required the syntax parsing and semantics for non-dependent types without instantiation. I asked why, and the answer was "to check for errors without needing to instantiate it." I responded with "of what use is checking it if it is never used or tested?" And that was the end of that.

> The implementation of this is hugely complicated and expensive to maintain

I quietly revolted and refused to implement that disaster. AFAIK there was never a problem with deferring parsing/semantic until instantiation.