On 07/04/2013 03:39 PM, Oleksiy wrote:
> 1. What is the rationale behind "prefix declaration" of an array? Using
> right-to-left order to declare an array and left-to-right order to
> access elements seems confusing.
It seems to be confusing to people who are used to C and C++'s
inside-out definition. In D, it is always "type and then the square
brackets".
> 2. Consider this code:
> dchar[3][5] arr = '.';
That is an array of 5 elements where the type of each element is dchar[3].
However, that is a confusing syntax because the right-hand side is not
the same type as the elements, which is dchar[3]. Perhaps D supports it
for C compatibility?
It doesn't match the following. Here, the right-hand side is the same as
the element type:
int[2] arr2 = 42;
assert(arr2 == [ 42, 42 ]);
But this doesn't compile:
char[3][5] arr = [ '.', '.', '.' ];
Error: mismatched array lengths, 15 and 3
I see that as a bug but can't be sure.
> arr[2][] = '!';
arr[2] is the third dchar[3] of arr. When [] is applied to it all of its
elements are set to '!'.
> writeln();
> writeln(arr);
>
> Result: ["...", "...", "!!!", "...", "..."]
Looks correct.
> Which is expected. According to Ali Çehreli's tutorial, omitting the
> index of an array will result in operation being applied to the whole
> array (in this case element of another array).
The book either fails to mention the term "array-wise" or does not use
it sufficiently but Ali Çehreli is correct in that arr[] means "all of
the elements of arr".
> change the code:
> - arr[2][] = '!';
> + arr[][2] = '!';
arr[] is a slice to all of the elements of arr. When [2] is applied to
it then you again get the third element.
> Still getting the same result: ["...", "...", "!!!", "...", "..."]
Still makes sense.
> I would expect to get: ["..!", "..!", "..!", "..!", "..!"]
Like C and C++, D does not have multi-dimensional arrays. You must do
that yourself. One of the most straight-forward is by foreach:
import std.stdio;
void main()
{
dchar[3][5] arr = '.';
foreach (ref e; arr) {
e[2] = '!';
}
writeln(arr);
}
["..!", "..!", "..!", "..!", "..!"]
> since omitted index would apply the operation to all elements of the
> first dimension of the array.
Sorry about that confusion but "a slice to all of the elements" and
"array-wise operation" syntaxes are very similar.
a[] alone is a slice to all of the elements of 'a'. When you use that
syntax in an operation, then that operation is applied "array-wise":
a[] = b[] + c[];
That is the same as
a[i] = b[i] + c[i]
for all valid values of 'i'.
Ali
