Compiling GCC With a C++ Compiler (g++)

[Gabriel Dos Reis]

Andreas Schwab <schwab@suse.de> writes:

| Gabriel Dos Reis <gdr@cs.tamu.edu> writes:
| 
| > If you can a strcture with const-qualified field, you can modify any
| > part, except that field.  (I'm talking of C here).
| 
| Yes, I'm also talking about C.  And in C you can have const qualified
| lvalues that ultimatively denote modifiable objects.

But, in the tree_string case, it is not a modifiable object.  See the
language I quoted in the other message.

| I can't see how it
| makes a difference that in this case it is declared as an array, since the
| underlying object is clearly writable.

It is not the fact that the field is declared an array, it is the fact
it is declared an array of *const* T.

Notice, Geoff made the following justification:

  The 'const' is there to indicate that the string should not be changed
  once the STRING_CST is created; STRING_CSTs may be shared.

but you can't have it both way: it can't be modifiable and
nonmodifiable.  C says that if any member is const-qualified, the
whole stuff becomes non-modifiable.  That put a several restriction on
how you can construct it.  Either through brace-enclosed
initializer-list or fiddlinig with bytes before giving the tree_string
type. 

Plus, this apply to the tree_node union too.  I believe we have
reached a point where the change is clearly a bug.

-- Gaby