On Thu, 06 Jan 2011 12:49:19 -0500, Max Samukha <spam...@d-coding.com>
wrote:
Some of us who have the knack of writing metaprograms in D know that
many algorithms can be implemented with both recursive templates and
CTFE. A simple example is map:
Recursive template instantiation:
template staticMap(alias pred, A...)
{
static if (A.length)
alias TypeTuple!(pred!(A[0]), staticMap!(A[1..$])) staticMap;
}
CTFE:
template staticMap(alias pred, A)
{
mixin("alias TypeTuple!(" ~ _staticMap(A.length) ~ ") staticMap;");
}
private string _staticMap(size_t len)
{
string result;
if (len)
{
result ~= "pred!(A[0])";
for(size_t i = 1, i < len; ++i)
{
result ~= ", pred!(A[" ~ to!string(i) ~ "])";
}
}
return result;
}
It is not easy to decide which approach to implement in a library
because both have drawbacks.
Can anybody give informed advice as to which one is preferable in
practice? Or should a library provide both?
You should prefer CTFE IMO. Templates can leave a trail of instantiated
templates in the exe. The compiler does not trim anything out that's only
used at compile time, but I think with CTFE it does not instantiate as
many templates. I'd guess the exe size would be significantly larger for
the template solution for a large number of elements.
-Steve
