Safety/purity and assert/enforce error messages

[Joseph Rushton Wakeling]

Hi all,

Suppose that I want to insert some variable values into an assert error message. 
  The easy way to do this is something like:

     assert(someCondition, text("x = ", x, ", cannot blah blah blah"));

However, the use of text() prevents me from applying @safe and other such 
attributes to the function containing this assert, even though text() will only 
be called in the event of an assertion failure.

Is there any reliable way to include variable values in the error message that 
doesn't interfere with @safe, pure, etc.?  Using to!string has a similar problem.

Thanks & best wishes,

     -- Joe