ctRegex with variable?

[Jethro via Digitalmars-d-learn]

Can regex's have variables in them? I'd like to create a ctRegex 
but match on runtime strings that are known at runtime.

e.g.,

auto c = ctRegex~("x{var}")

where var is a variable that is passed at runtime. e.g., match(s, 
c, "test") will replace var with test.

The reason is I basically have the same regex to match but each 
one differs in a specific way. It would be nice to be able to use 
a fast way to search since most of the regex is the same but only 
the a single token differs(and these tokens are only known at 
runtime).

I obviously can build the regex string at runtime like

auto var = "test"
auto c = Regex("x{"~var~"}");

or whatever... but this is much slower when only var changes.