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C++11 lambda functions capture variables declared in their outer scope by value-copy or by reference. This means that value members of a lambda cannot be move-only types. [13] C++14 allows captured members to be initialized with arbitrary expressions. This allows both capture by value-move and declaring arbitrary members of the lambda, without ...
The first treats all lambda abstractions as defining anonymous functions. The second, treats lambda abstractions which are applied to a parameter as defining a function. Lambda abstractions applied to a parameter have a dual interpretation as either a let expression defining a function, or as defining an anonymous function.
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
initialization of an additional variable within a range-based for statement [16] lambdas in unevaluated contexts [17] [18] default constructible and assignable stateless lambdas [17] [19] allow pack expansions in lambda init-capture [17] [20] class types in non-type template parameters, also allowing string literals as template parameters [21]
Like function definitions, blocks can take arguments, and declare their own variables internally. Unlike ordinary C function definitions, their value can capture state from their surrounding context. A block definition produces an opaque value which contains both a reference to the code within the block and a snapshot of the current state of ...
The names "lambda abstraction", "lambda function", and "lambda expression" refer to the notation of function abstraction in lambda calculus, where the usual function f (x) = M would be written (λx. M), and where M is an expression that uses x. Compare to the Python syntax of lambda x: M.
The C programming language historically avoids the main difficulty of the funarg problem by not allowing function definitions to be nested; because the environment of every function is the same, containing just the statically allocated global variables and functions, a pointer to a function's code describes the function completely.
The variable b is needed here to meet Java's requirement that variables referenced from within a lambda expression be effectively final. This is an inefficient program because this implementation of lazy integers does not memoize the result of previous calls to eval. It also involves considerable autoboxing and unboxing.