On Friday, January 31, 2020 5:43:44 AM MST MoonlightSentinel via Digitalmars-d-learn wrote: > On Friday, 31 January 2020 at 12:37:43 UTC, Adnan wrote: > > What's causing this? > > You mixed up the array lengths: > > const int[3][2] matA = [[0, -1, 2], [4, 11, 2]]; > const int[2][3] matB = [[3, -1], [1, 2], [6, 1]]; > > matA is an SA containing <2> elements of type int[3]. > matB is an SA containing <3> elements of type int[2].
Specifically, the dimensions are read outwards from the variable name, so on the left-hand side, that means that they go right-to-left, whereas on the right-hand side, they go left-to-right. This is consistent with how it works with types in C/C++ except that there, they put the dimensions for static arrays on the right-hand side of the variable name, meaning that while you have to read stuff like pointer types from left-to-right in C/C++, you don't have to do that with static arrays. Ultimately, what D is doing is consistent but confusing. e.g. For C/C++ int** foo; // A pointer to a pointer to an int int foo[5][2]; // A 5 dimensional array of two dimensional arrays of int foo[4][1] = 7; and for D: int** foo; // A pointer to a pointer to an int int[2][5] foo; // A 5 dimensional array of two dimensional arrays of int foo[4][1] = 7; For C/C++, you often don't realize how the rules work until you have to read function pointers, because they put the static array lengths no the right-hand side, and they actually allow you to put stuff like const in multiple places instead of only in the place where it would be right right-to-left. e.g. if the rule were followed strictly, const int i = 0; wouldn't be legal in C/C++. Rather, it would have to be int const i = 0; In reality, both work, but people end up using the first one. So, ultimately, it adds to the confusion when dealing with more complex tyypes. D doesn't have that problem, but since it used parens with type qualifiers, it forces const to go on the left, making it less consistent. e.g. const int i = 0; or const(int) i = 0; So, neither C/C++ nor D is entirely consistent, but the basic rule is that types are read outwards from the variable name, which is why you get the weirdness with static array dimensions in D. - Jonathan M Davis
