On Sunday, 27 May 2018 at 20:38:25 UTC, Daniel Kozak wrote:
I would rewrite it to something like this:
template BTree(ValueT, KeyT = ValueT,alias KeyF =
unaryFun!"cast(const)a")
{
class BTree
{
This is roughly what I originally had, but it creates a number of
problems that I wanted to get around. Changing KeyF back to an
alias means that any function that uses it can no longer be
const, pure, @nogc, or nothrow. Essentially the parameter is
just anything the user provides.
If I use a template value-parameter, then it forces any lambda
the user passes in to either match the type I enter in (with
const, pure, etc.) or the program to fail to compile. That is, I
don't want the user to pass in any function, but only functions
with the desired attributes. I.e., I wouldn't want them to pass
in for KeyF something like "a.data--".
Listing out the full type does indeed work correctly with various
examples, and letting the user pass in something like `a =>
a._id` does compile, but the only problem is that when there are
two such template instances in the same program.
Logically `BTree!(MyStruct, int, a => a.id)`,
`BTree!(AnotherStruct, char, a => a.name[0])`, `BTree!int` and
`BTree!char` should all be totally independent. But for reasons
unknown, the individual parameters seems to be swapped and and
confused during compilation.
In the error above I listed. The function parameter from
`BTree!char` is being used to create a compile error against
`BTree!int`, which is very odd. Each of these classes compile
and run just fine individually, the compilation only breaks when
both exist.
