bug.d ---------------->8---------------->8---------------- @trusted: import std.datetime : benchmark; import std.stdio : writefln, writeln;
alias double Real; void ben(alias fun)(string msg, uint n = 1_000_000) { auto b = benchmark!fun(n); writefln(" %s %s ms", msg, b[0].to!("msecs", int)); } struct Matrix(int row, int col) { private: alias row Row; alias col Col; alias Real[Row * Col] Data; public: Data _data = void; alias _data this; this(const Real[Row*Col] data) pure nothrow { _data = data; } } M inverse(M)(const auto ref M m) { writeln(m[]); M minv = m; return minv; } unittest { alias Matrix!(4, 4) Matrix4x4; auto m9 = Matrix4x4([4, 0, 0, 0, 0, 0, 2, 0, 0, 1, 2, 0, 1, 0, 0, 1]); ben!( {auto r = inverse(m9);} )("4x4 inverse:"); } ----------------8<----------------8<---------------- t1.d ---------------->8---------------->8---------------- import std.stdio; void main(){ } ----------------8<----------------8<---------------- It took me a long time to pinpoint this because it's tricky to trigger the bug. Once you have those two files, compile with this: dmd -unittest t1.d bug.d and then run t1: ./t1 The output you get should look like this: ... [0, 4, 0, 0, 0, 0, 0, 2, 0, 0, 1, 2, 0, 1, 0, 0] Obviously the output is wrong. 'm9' for some reason is getting overwritten. In my project this caused big problems because there are other m# with different values, and their values would literally get copied to m9. Calling inverse() on m9 then would fail because the other matrices are not invertible. Placing a writeln() in inverse() helped me realize that what was being passed to inverse() was being modified somewhere. I'm still now sure how m9 is being modified. Another point, compiling with this: dmd -unittest bug.d t1.d and then running bug: ./bug doesn't trigger the bug. Could someone else please confirm this behavior?