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I am not suggesting the example in the article is bad. It shows what is a closure. And I am still waiting to see what is a difference. I can't find this anywhere yet. Finally, a function object is certainly not limited to object-oriented languages. I think it's an old concept originated in functional programming. Maybe I am missing something. -- [[User:TakuyaMurata|Taku]] 11:41, Jun 8, 2005 (UTC)
: A function object is something you create in object-oriented programs to make up for the lack of proper first-class and higher-order functions (i.e. closures). OOP languages that support closures (e.g. [[Smalltalk]]) typically do not use function objects (as shown in the example), because the presence of closures removes the need for function objects. However, as closures in such languages (e.g. Smalltalk blocks) are modelled as objects, they do resemble function objects. But the typical languages where function objects are used (such as C++ and Java) do not support lexical environment closure, and thus function objects are not equivalent and not even related. The key feature of a closure is the environment link. A function object in C++ can be best compared to a function pointer in C, in that it can be invoked and passed around dynamically. Closures are not supported in C++ because the language's activation record model is entirely stack-based. Java anonymous inner classes fix this halfway by providing syntactic sugar for using final variables in the closure, but these are in fact translated to parameters to the anonymous class. So to summarize: a function object is an object that behaves semantically (and sometimes syntactically) like a function, whereas a closure is a function extended with its environment of definition. Some function objects may be in fact closures, and some closures may in fact be objects (Smalltalk blocks), which means the two concepts ''may'' overlap. But they definately don't have to. [[User:Wlievens|Wouter Lievens]] 12:43, 8 Jun 2005 (UTC)
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