On Tue, Apr 5, 2011 at 4:52 PM, Lorenzo Caminiti <lorcaminiti@gmail.com>wrote:
On Sun, Apr 3, 2011 at 2:22 PM, Steven Watanabe <watanabesj@gmail.com> wrote:
AMDG
On 04/03/2011 11:13 AM, Lorenzo Caminiti wrote:
Boost.Local uses a special name `this_` to access the object `this` bound from the enclosing scope. Shall this name be `this_` or `_this` according to Boost practices?
struct c { void g(int x) { ... } void f() { void BOOST_LOCAL_FUNCTION_PARAMS( (int x) (bind this) ) { this_->g(x); //<<<<<<<<< Shall this be `_this->g(x);` instead? ... } BOOST_LOCAL_FUNCTIO_NAME(l) ... } ... };
In particular, some library uses _ postfix for statements like mpl::if_ (not mpl::_if) while other uses _ prefix for variables like phoenix::local_names::_f (not local_names::f_).
The convention is that _xxx is used for placeholders. xxx_ is used when xxx is a keyword.
1) What is the exact definition of a "placeholder"?
My guess: Any object that gets implicitly bound upon the evaluation of its enclosing expression.
2) What is the convention for an xxx that is both a keyword and a placeholder?
My guess: Just use a leading underscore, as then it isn't a keyword anymore, so no need for a trailing underscore. I wouldn't consider your bound "this" variable *implicitly* bound, as it appears explicitly in the bind list, so I'm partial to "this_" (trailing underscore only). I also believe some variant of "this" is better than other suggestions like "that" and "self", because: - The bind list should use the keyword "this" to bind the current object, as that's the *only* thing "this" could mean. Any other keyword you choose *could* happen to be a local variable that the user *could* want to bind instead, and they'd be SOL. - The keyword used in the function body should match (as closely as possible) the keyword used in the bind list. Also, additional suggestion, but probably not a good one: You could provide a macro for any user to introduce a new name for the "this" variable within a Boost.Local block, similar to Boost.Tribool's macro that allows one to introduce a new name for the 3rd tribool state. So if one prefers "self", "_this", "this_", "that", etc., they will be free to do so. Of course, introducing multiple names for the same thing can easily make things confusing... - Jeff