import std.stdio; class Foo { double x; this(double x) { this.x = x; } } void main() { auto ifoo = new invariant(Foo)(0.); auto foo = new Foo(0.); writeln(foo.x); writeln(ifoo.x); // <- Error } causes this compiler output : /usr/local/bin/../src/phobos/std/format.d(2048): Error: no property 'toString' for type 'invariant(double)' /usr/local/bin/../src/phobos/std/format.d(2049): template std.stdio.PrivateFileWriter!(char).PrivateFileWriter.write(C) does not match any function template declaration /usr/local/bin/../src/phobos/std/format.d(2049): template std.stdio.PrivateFileWriter!(char).PrivateFileWriter.write(C) cannot deduce template function from argument types !()(int) Segmentation fault
The problem is the following code: } else static if (is(const D == const(float)) || is(const(D) == const(double)) || is(const(D) == const(real))) { // Do stuff. } else // Similar stuff for more types. The problem is that const(immutable(T)) seems to evaluate to immutable(T), not const(T), as the following program demonstrates: import std.stdio; void main() { immutable real foo = 1.0L; alias const(typeof(foo)) T; writeln(T.stringof); // Prints immutable(real). } This can probably be fixed by changing is(const(T) == const someType) tests to is(immutable(T) == immutable someType).
Created attachment 294 [details] Patch for std.format problems. Here's a patch that does what I suggested previously. It seems to solve the problem, and all of the std.format unittests still pass, except for the ones on lines 2462 and 2464, which don't pass even without the patch.
This was fixed between 2.026 and 2.030. I believe the segfault was fixed in 2.027.