dsimcha wrote:
== Quote from Jacob Carlborg (d...@me.com)'s article
On 10/12/09 23:49, dsimcha wrote:
I'm working on a mathematical expression interpreter for D, which would allow
for closed form mathematical expressions to be specified as string literals at
runtime and be evaluated. For example:
MathExp myExpression = mathExp("x^2 + e^cos(-x) - 2 * sqrt(pi)", "x");
writeln(myExpression(2)); // Does exactly what you think it does.
I've found the syntax so convenient that I'd like to transparently specialize
it on strings known at compile time. The idea is that, when the expression is
hard-coded, you will still be able to use the MathExp interface, but your
expression will evaluate at the full speed of a statically compiled function.
Is there any way to test whether the value of an argument to a template
function is known at compile time and specialize on this?
Doesn't all values to a template have to be known at compile time
No, I mean the *function* parameters of a template function.
I may be wrong, but I seem to remember reading somewhere that DMD always
tries to evaluate as much as possible at compile time. That is, if a
function is CTFE-enabled, and its input is known at compile time, it is
calculated at compile time.
void main(string[] args) {
auto x = foo(args[1]); // foo() is evaluated at run time
auto y = bar("baz"); // foo() is evaluated at compile time
}
That said, I also seem to remember that the use of structs and classes
is very limited (or nonexistent) in CTFE, and I guess your mathExp() is
supposed to return a MathExp struct...
-Lars
