Why this code can't take advantage from CTFE?

[Marc Schütz via Digitalmars-d-learn]

On Wednesday, 3 February 2016 at 16:07:59 UTC, Messenger wrote:
> What is a good way to try to force it? Using enum? Then 
> optionally copying the value once to avoid the "manifest 
> constant" copy/paste behaviour, where applicable?

template forceCTFE(alias expr) {
     alias forceCTFE = expr;
}

auto value = forceCTFE!(some_expression());