The Matlab C headers provide some kind of hand-crafted contracts by defining extra functions with suffix "_d" that check all the arguments and then detouring the calls to the original functions via the preprocessor (#define foo foo_d) I tried to leverage D's built-in contract programming but it doesn't work: module externcontracts; import externcontracts2; void foo(int a) in {assert(a>=0);} module externcontracts2; void foo(int a){} yields: externcontracts.d(3): Error: function externcontracts.foo in and out contracts require function body resp. externcontracts.d(3): missing body { ... } after in or out if you put a ';' after the in{} block Note that this is exactly the same syntax as for interface contracts.
What is the expected use and effect of the code show? (Not sure I'm getting it.) With or without contracts, externcontracts.foo and externcontracts2.foo are distinct functions, so automatic forwarding from one another won't happen. One obvious workaround would be: module externcontracts; import externcontracts2; void foo(int a) in {assert(a>=0);} { return externcontracts2.foo(a); } which may be automated in a number of ways (introspection, mixin etc).
No clarification in 4 years, closing :)