Pony ORM author is here. Pony translates Python generator into SQL query in three steps: Decompiling of generator bytecode and rebuilding generator AST (abstract syntax tree) Translation of Python AST into “abstract SQL” — universal list-based representation of a SQL query Converting abstract SQL representation into specific database-dependent SQL dialect The most complex part is … Read more
Updated Now with improved recursion depth! Works on MSVC10 and GCC without increased depth. 🙂 Simple compile-time recursion + addition: template<unsigned Cur, unsigned Goal> struct adder{ static unsigned const sub_goal = (Cur + Goal) / 2; static unsigned const tmp = adder<Cur, sub_goal>::value; static unsigned const value = tmp + adder<sub_goal+1, Goal>::value; }; template<unsigned Goal> … Read more
NSString *name = NSStringFromClass ([NSArray class]); You can even go back the other way: Class arrayClass = NSClassFromString (name); id anInstance = [[arrayClass alloc] init];
send sends a message to an object instance and its ancestors in class hierarchy until some method reacts (because its name matches the first argument). Practically speaking, those lines are equivalent: 1.send ‘+’, 2 1.+(2) 1 + 2 Note that send bypasses visibility checks, so that you can call private methods, too (useful for unit … Read more
Funny, I’ve just written a function_traits implementation based on Specializing a template on a lambda in C++0x which can give the parameter types. The trick, as described in the answer in that question, is to use the decltype of the lambda’s operator(). template <typename T> struct function_traits : public function_traits<decltype(&T::operator())> {}; // For generic types, … Read more
If you want indentation in terms of nesting level rather than spaces and tabs, things get tricky. For example, in the following code: if True: print( get_nesting_level()) the call to get_nesting_level is actually nested one level deep, despite the fact that there is no leading whitespace on the line of the get_nesting_level call. Meanwhile, in … Read more
I haven’t seen anything to match the elegance of Scott Schurr’s str_const presented at C++ Now 2012. It does require constexpr though. Here’s how you can use it, and what it can do: int main() { constexpr str_const my_string = “Hello, world!”; static_assert(my_string.size() == 13, “”); static_assert(my_string[4] == ‘o’, “”); constexpr str_const my_other_string = my_string; … Read more
I like using SFINAE to check boolean conditions. template<int I> void div(char(*)[I % 2 == 0] = 0) { /* this is taken when I is even */ } template<int I> void div(char(*)[I % 2 == 1] = 0) { /* this is taken when I is odd */ } It can be quite useful. … Read more
The block that you pass to define_method can include some parameters. That’s how your defined method accepts arguments. When you define a method you’re really just nicknaming the block and keeping a reference to it in the class. The parameters come with the block. So: define_method(:say_hi) { |other| puts “Hi, ” + other }
This changed as of the ES2015 (aka “ES6”) specification: JavaScript now has proxies. Proxies let you create objects that are true proxies for (facades on) other objects. Here’s a simple example that turns any property values that are strings to all caps on retrieval, and returns “missing” instead of undefined for a property that doesn’t … Read more