cplusplus-th
============
`cplusplus-th` allows you to foreign import C++ functions that are
compatible with the `ccall` calling convention. It also includes
some standard library abstractions.
Example
-------
With the following C++ function in the object file `cbits/string.o`:
```c++
namespace haskell {
string* fromCString(char const* x, int length) {
return new string(x, length);
}
}
```
We can import it into Haskell with:
```haskell
cplusplus "haskell::fromCString(char const*, int)" "cbits/string.o"
[t|CString -> Int -> IO Std__basic_string|]
```
Building
--------
It works by looking up the symbol in the object file.
When using cabal, it is recommended you include the C++ file in
your `c-sources` and compile it in a build hook. For example:
```haskell
import Distribution.Simple
import Distribution.Simple.Setup
import Distribution.Simple.Program
import Distribution.Simple.Program.Types
import Distribution.Simple.LocalBuildInfo
import Distribution.PackageDescription
cc_flags = ["-stdlib=libc++", "-o", "cbits/string.o", "-c", "cbits/string.cc"]
main :: IO ()
main = defaultMainWithHooks simpleUserHooks {
buildHook = buildCPlusPlus
}
buildCPlusPlus :: PackageDescription -> LocalBuildInfo -> UserHooks -> BuildFlags -> IO ()
buildCPlusPlus pkg buildInfo hooks flags = do
let verb = fromFlag (buildVerbosity flags)
clang <- findProgramLocation verb "clang++"
let clang' = case clang of
Just x -> x
Nothing -> error "clang++ not on path"
runProgram verb (simpleConfiguredProgram "clang++" (FoundOnSystem clang')) cc_flags
buildHook simpleUserHooks pkg buildInfo hooks flags
```
Standard Library
----------------
`Foreign.CPlusPlusStdLib` exports the following type class:
```haskell
class CPlusPlusLand a {- haskell side -} b {- c++ side -} where
to :: a -> IO b
from :: b -> IO a
```
To avoid orphan instances, it implements instances for
some numeric types, `String` and `ByteString`.
Compatability
-------------
- Static functions are simply the arguments.
- Static member functions take the object as the first argument.
- Functions via a vtable are not possible.
- Inline functions are not possible.
- instantiating templates is not possible.