[Issue 6857] Precondition contract checks should be statically bound.

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6857



--- Comment #63 from Walter Bright <bugzilla at digitalmars.com> 2012-05-07 08:29:21 PDT ---
(In reply to comment #61)
> (In reply to comment #58)
> > It's not that simple. Several considerations have to be met:
> > 
> > 1.  Because of struct construction/destruction, you really only 
> > want to construct the parameter list *once*, but you're calling two 
> > functions with the same parameter list.
> 
> Can't this be solved by simply making all struct parameters to the in/out
> functions ref?

Losing all C ABI compatiblity in the process.

> I assume these were part of the reason for using nested functions to implement
> contract inheritance.  2 is indeed something that needs to be considered.  But
> is forwarding the arguments any more difficult than putting the arguments onto
> the stack in the first place?

How do you forward a variadic function? You don't know what's on the stack to
forward.

> class A {
>     void foo_in(int n) {  assert(n>0); }
>     int foo_dbc(int n) { foo_in(this, n); return foo(n); }
>     virtual int foo(int n) { return n; }
> }
> 
> then a call to foo would translate to a call to foo_dbc when compiling in
> non-release mode.  This also has the advantage of not changing the vtable
> layout.

Again, you're pushing the parameters on the stack twice - and this won't work
for variadic functions.

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