Some comments in
https://reviews.llvm.org/rGfd89af6880f33ead708abe2f7d88ecb687d4e0d2
<https://reviews.llvm.org/rGfd89af6880f33ead708abe2f7d88ecb687d4e0d2> prompted
me to look more into potential simplifications of our EditLine wrapper and I
wanted to run this by anyone who is interested before making the changes.
Right now we set a bunch of callbacks in libedit that are captureless lambdas
implicitly converted to C function pointers. The lambdas look up an instance
of our Editline class and invoke member functions. The boilerplate that could
be generated by templates is something like the following:
class Foo { // Imagine this is our Editline class that wraps libedit
public:
unsigned char Foo1(int ch) { // These are member functions invoked by
lambdas we pass to libedit
return 'a';
}
unsigned char Bar(int ch) {
return 'b';
}
unsigned char Baz(int ch) {
return 'c';
}
};
typedef unsigned char (*elFnPtr)(EditLine*, int); // Signature of callbacks
libedit takes (note Edit__L__ine is libedit, and Edit__l__ine is our wrapper)
typedef unsigned char (Foo::*FooMemPtr)(int ch); // Signature of member
functions invoked
template<FooMemPtr callback, typename Fn = elFnPtr>
tuple<const char*, const char*, Fn> createEditLineCommandDescriptor(const char*
command, const char* helpText) {
return make_tuple(command, helpText, [] (EditLine*, int ch) {
cout << ch;
Foo foo;
((&foo)->*callback)('a');
return (unsigned char) ch;
});
}
auto editlineCommands = {
createEditLineCommandDescriptor<&Foo::Foo1>(“Command1", “Command1 help"),
createEditLineCommandDescriptor<&Foo::Bar>(“Command2", “Command2 help")
};
for (auto editlineCommand : editLineCommands) {
// call into libedit to add editlineCommand, e.g.:
el_set(EL_ADDFN, editlineCommand.get<0>(), editLineCommand.get<1>(),
editLineCommand.get<2>());
}
The pointer to member function is a type parameter because otherwise the
compiler complains about the lambda needing to capture it, in which case we
could not pass it to libedit.
I also plan to look into the wchar_t/char preprocessor logic that the original
comment brought up but then I got distracted by shiny template stuff ;-)
Thanks!
Neal_______________________________________________
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