On Monday, 8 February 2021 at 13:09:53 UTC, Rumbu wrote:
On Monday, 8 February 2021 at 12:19:26 UTC, Basile B. wrote:
On Monday, 8 February 2021 at 11:42:45 UTC, Vindex wrote:
size_t ndim(A)(A arr) {
return std.algorithm.count(typeid(A).to!string, '[');
}
Is there a way to find out the number of dimensions in an
array at compile time?
yeah.
---
template dimensionCount(T)
{
static if (isArray!T)
{
static if (isMultiDimensionalArray!T)
{
alias DT = typeof(T.init[0]);
enum dimensionCount = dimensionCount!DT + 1;
}
else enum dimensionCount = 1;
}
else enum dimensionCount = 0;
}
///
unittest
{
static assert(dimensionCount!char == 0);
static assert(dimensionCount!(string[]) == 1);
static assert(dimensionCount!(int[]) == 1);
static assert(dimensionCount!(int[][]) == 2);
static assert(dimensionCount!(int[][][]) == 3);
}
---
that can be rewritten using some phobos traits too I think,
but this piece of code is very old now, more like learner
template.
dimensionCount!string should be 2.
My take without std.traits:
template rank(T: U[], U)
{
enum rank = 1 + rank!U;
}
template rank(T: U[n], size_t n)
{
enum rank = 1 + rank!U;
}
template rank(T)
{
enum rank = 0;
}
Here's the version I actually wanted to write:
---
enum rank(T) = is(T : U[], U) ? 1 + rank!U : 0;
---
But it's not possible, because of 2 language limitations:
1. Ternary operator doesn't allow the different branches to be
specialized like `static if` even if the condition is a
compile-time constant.
2. `is()` expressions can only introduce an identifier if inside
a `static if`.
Otherwise, I'd consider this the "idiomatic" / "typical" D
solution, since unlike C++, D code rarely (*) overloads and
specializes templates.
(*) Modern Phobos(-like) code.
---
template rank(T)
{
static if (is(T : U[], U))
enum rank = 1 + rank!U;
else
enum rank = 0;
}
unittest
{
static assert( rank!(char) == 0);
static assert( rank!(char[]) == 1);
static assert( rank!(string) == 1);
static assert( rank!(string[]) == 2);
static assert( rank!(string[][]) == 3);
static assert( rank!(string[][][]) == 4);
}
---
Otherwise, the shortest and cleanest solution IMO is this one:
---
enum rank(T : U[], U) = is(T : U[], U) ? 1 + rank!U : 0;
enum rank(T) = 0;
unittest
{
static assert( rank!(char) == 0);
static assert( rank!(char[]) == 1);
static assert( rank!(string) == 1);
static assert( rank!(string[]) == 2);
static assert( rank!(string[][]) == 3);
static assert( rank!(string[][][]) == 4);
static assert( rank!(char) == 0);
static assert( rank!(char[1]) == 1);
static assert( rank!(char[1][2]) == 2);
static assert( rank!(char[1][2][3]) == 3);
static assert( rank!(char[1][2][3][4]) == 4);
}
---
- Use eponymous template syntax shorthand
- Static arrays are implicitly convertible to dynamic arrays, so
we can merge the two implementations.
