Tested with: D2.068.1 and D2.069.b struct Foo { this( float x_, float y_ ) { // option A //x = x_; //y = y_; // option B v[0] = x_; v[1] = y_; } union { struct { float x = 0; float y = 0; } float[2] v; } } struct Bar { Foo foo = Foo( 1, 2 ); } Bar bar; Bar baz = bar.init; printf( "bar: %f, %f\n", bar.foo.x, bar.foo.y ); printf( "baz: %f, %f\n", baz.foo.x, baz.foo.y ); ------------------------------------------------- prints (with option B): bar: 0.000000, 0.000000 // BUG?? baz: 1.000000, 2.000000 prints (with option A): bar: 1.000000, 2.000000 baz: 1.000000, 2.000000
Note: before https://github.com/D-Programming-Language/dmd/pull/2681 this caused a compile-time error: test.d(29): Error: duplicate union initialization for v Perhaps this should still result in an error due to incomplete implementation of unions in CTFE.
Encountered what seems to be the same issue. Reproduces on DMD 2.084.0 and LDC 1.13.0 import std.stdio; struct Foo { static Foo initializedFoo() { Foo x; x.a_array[0] = 1; return x; } union { float a; float[1] a_array; } } Foo bar = Foo.initializedFoo(); void main() { writeln(bar.a); writeln(bar.a_array); } returns nan [nan] instead of 1 [1]
*** Issue 18313 has been marked as a duplicate of this issue. ***
Just helping out someone in discord, and ran into what looks like the same issue. What seems to happen is if the non-first union member is a static array, and that array is set via indexing items, then it does not set the internal tag for the union during CTFE, so it doesn't think the second member is set, and instead writes out the first member. Change option B to: ```d v = v.init; v[0] = x_; v[1] = y_; ``` and it works. What I think happens is the assignment to v sets the union tag. If you set v all at once, it also works: ```d v = [x_, y_]; ``` I think the compiler should detect the initialization via the indexed usage and set the tag properly.