It is equivalent but not identical. Simply said, if a lambda expression does not capture values, it will be a singleton that is re-used on every invocation. The behavior is not exactly specified. The JVM is given big freedom on how to implement it. Currently, Oracle’s JVM creates (at least) one instance per lambda expression … 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
It is strange how much beauty varies for different people. I find the list comprehension much clearer than filter+lambda, but use whichever you find easier. There are two things that may slow down your use of filter. The first is the function call overhead: as soon as you use a Python function (whether created by … Read more
Lambda comes from the Lambda Calculus and refers to anonymous functions in programming. Why is this cool? It allows you to write quick throw away functions without naming them. It also provides a nice way to write closures. With that power you can do things like this. Python def adder(x): return lambda y: x + … Read more
Mine would be this in c# 3.0 🙂 var type = typeof(IMyInterface); var types = AppDomain.CurrentDomain.GetAssemblies() .SelectMany(s => s.GetTypes()) .Where(p => type.IsAssignableFrom(p)); Basically, the least amount of iterations will always be: loop assemblies loop types see if implemented.
… starting in Java SE 8, a local class can access local variables and parameters of the enclosing block that are final or effectively final. A variable or parameter whose value is never changed after it is initialized is effectively final. For example, suppose that the variable numberLength is not declared final, and you add … Read more
When you want to treat lambda expressions as expression trees and look inside them instead of executing them. For example, LINQ to SQL gets the expression and converts it to the equivalent SQL statement and submits it to server (rather than executing the lambda). Conceptually, Expression<Func<T>> is completely different from Func<T>. Func<T> denotes a delegate … Read more
Well, you can use Expression.AndAlso / OrElse etc to combine logical expressions, but the problem is the parameters; are you working with the same ParameterExpression in expr1 and expr2? If so, it is easier: var body = Expression.AndAlso(expr1.Body, expr2.Body); var lambda = Expression.Lambda<Func<T,bool>>(body, expr1.Parameters[0]); This also works well to negate a single operation: static Expression<Func<T, … Read more
If you have Guava in your project, you can use the Streams.zip method (was added in Guava 21): Returns a stream in which each element is the result of passing the corresponding element of each of streamA and streamB to function. The resulting stream will only be as long as the shorter of the two … Read more
The compiler declares the variable in a way that makes it highly prone to an error that is often difficult to find and debug, while producing no perceivable benefits. Your criticism is entirely justified. I discuss this problem in detail here: Closing over the loop variable considered harmful Is there something you can do with … Read more