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I do not know much about OO-languages, but from what I have seen, it seems most class-based OO-languages uses a keyword new (or something equivalent) to create an object. Prototype-based OO-languages like JavaScript even fake it.

From a viewpoint of keeping the syntax simple, why not leave out the new keyword and use only the constructor (typically of the same name as the class)?

Is there any semantic consideration involved in prefixing the constructor with a new keyword?

I have noticed that in Scala, if you define a case-class, you can simply use the constructor without a preceding new to create an object, while for other classes, you have to use new. I do not know the reason. I mention it simply because it may be related.

oɔɯǝɹ
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reflectionalist
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    Did you have a look at Python? It works exactly the way you suggested - without the new keyword. I guess most languages using "new" as a keyword just inherited that from C++ for historical reasons. – Doc Brown Jan 03 '15 at 09:40
  • In Delphi / Object Pascal you call the constructor directly: myClass := TMyClass.Create; – oɔɯǝɹ Jan 03 '15 at 10:00
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    In C++ and JavaScript it's syntactically important. But even in languages where it could have been left out, don't you think it makes for more descriptive (self-documenting) code? If I write `List()` is it creating a list, or is it listing something (noun or verb)? If I write `new List()` the ambiguity goes away. – Hey Jan 03 '15 at 10:27
  • In Java, it is possible for class X to contain a method X that cannot be distinguished by its parameter list from an X constructor. "new" distinguishes object creation from method invocation. – Patricia Shanahan Jan 03 '15 at 10:52
  • @PatriciaShanahan I guess you could avoid that with explicit `this`, couldn't you? I think "new distinguishes object creation from method invocation" is exactly the point, though... not necessarily just for the compiler/interpreter, but also for the developer. – Hey Jan 03 '15 at 11:53
  • @Hey: Which leads to the obvious question: why should object creation be distinct from method invocation? `List()` is a terrible name for a method. – DeadMG Jan 03 '15 at 12:16
  • Why would anyone ever want a non-constructor function that looks like a constructor? – Weaver Jan 03 '15 at 12:38
  • @DeadMG Why is List a terrible name for a method (other than annoying StudlyCaps)? If I have something like an "AuctionItem" and I want to *list* it at auction, what should I call that action? Whether object creation and method invocation should be separate is good question. In languages like Lua I sometimes write a function that creates objects and I always find myself wanting to write `new` unless I name it like `createFoo`. Just two different ways of looking at the same problem I guess. – Hey Jan 03 '15 at 13:14

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As far as I know, it's simply a question of C++ having this syntax (and it needed some syntax because the language was not strong enough to support implementing new T(); at that time as a library) and then inherited. From memory, Java inherited it from C++, JavaScript picked it up from Java, and so did C#. Since then, it seems to have become pretty standard.

Fundamentally, it's no different to using curly braces to denote scope- it was inherited from a common ancestor.

DeadMG
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