Re: Cannot implicitly convert expression [[0, -1, 2], [4, 11, 2]] of type int[][] to const(int[2])[]
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
Re: Cannot implicitly convert expression [[0, -1, 2], [4, 11, 2]] of type int[][] to const(int[2])[]
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].
Cannot implicitly convert expression [[0, -1, 2], [4, 11, 2]] of type int[][] to const(int[2])[]
https://wiki.dlang.org/Dense_multidimensional_arrays#Static_arrays describes a way to create static arrays: int[3][3] matrix = [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]; However my complains that I can't implicitly create static arrays from dynamic arrays. private T[R1][C2] loopMul(ulong R1, ulong C1, ulong R2, ulong C2, T)( auto ref T[R1][C1] matrixA, auto ref T[R1][C2] matrixB) if (C1 == R2) { T[R1][C2] result; for (ulong r = 0; r < R1; ++r) { for (ulong c = 0; c < C2; ++c) { T toAdd = 0; for (ulong n = 0; n < C1; ++n) { toAdd += matrixA[r][n] + matrixB[c][n]; } result[r][c] = toAdd; } } } void main() { import std; scope (success) std.writeln("loopMul -- ok"); // assert([[0, -1, 2], [4, 11, 2]].loopMul!(2, 3, 3, 2, int)([[3, -1], [1, 2], [6, 1]]) == [ // [11, 0], [35, 20] // ]); const int[2][3] matA = [[0, -1, 2], [4, 11, 2]]; const int[3][2] matB = [[3, -1], [1, 2], [6, 1]]; const int[2][2] matC = [[11, 0], [35, 20]]; assert(matA.loopMul(matB) == matC); } /// I would share the D online editor link but `shorten` button doesn't do anything onlineapp.d(24): Error: cannot implicitly convert expression [[0, -1, 2], [4, 11, 2]] of type int[][] to const(int[2])[] onlineapp.d(25): Error: cannot implicitly convert expression [[3, -1], [1, 2], [6, 1]] of type int[][] to const(int[3])[] onlineapp.d(27): Error: template onlineapp.loopMul cannot deduce function from argument types !()(const(int[2][3]), const(int[3][2])), candidates are: onlineapp.d(1):loopMul(ulong R1, ulong C1, ulong R2, ulong C2, T)(auto ref T[R1][C1] matrixA, auto ref T[R1][C2] matrixB) What's causing this?