Bug 7180 – Documentation bug of "Const and Invariant Structs"

From http://d-programming-language.org/struct.html > Const and Invariant Structs > > A struct declaration can have a storage class of const, immutable or shared. > It has an equivalent effect as declaring each member of the struct as const, > immutable or shared. > > const struct S { int a; int b = 2; } > > void main() { > S s = S(3); // initializes s.a to 3 > S t; // initializes t.a to 0 > t = s; // ok, t.a is now 3 // (line 6) > t.a = 4; // error, t.a is const // (line 7) > } Current dmd (2.058head) raises following errors against the sample code: test.d(6): Error: variable test.main.t cannot modify const test.d(7): Error: can only initialize const member a inside constructor Because the definition of S is internally translated to: struct __S { int a; int b = 2; } alias const(__S) S; But, if you replace the definition to struct S { const int a; const int b = 2; } the compilation still raises: test.d(6): Error: variable test.main.t cannot modify struct with immutable members test.d(7): Error: can only initialize const member a inside constructor Because mutable object that has non-mutable members is "not assignable", then t = s is invalid, even if t and s are mutable S. Finally I think this is documentation bug.

The documentation was recently fixed.