If a struct is a value type why can I new it?

Question

In C# structs are value types, but I am able to new them as if they are reference types. Why is this?

A constructor is really just a method that gets the special privilege of messing with an object before it is considered initialized. — Tory, Mar 23 '13 at 18:29

score 42 · Accepted Answer · answered Mar 23 '13 at 17:56

42

Because they have constructors.

The new operator doesn't mean "this is a reference type"; it means "this type has a constructor". When you new something you create an instance, and in doing so you invoke a constructor.

For that matter, all value and reference types have constructors (at the very least a default constructor taking no args if the type itself doesn't define any).

answered Mar 23 '13 at 17:56

BoltClock

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Thanks. For Java, is "all value and reference types have constructors" also true? – Oct 30 '17 at 20:59
@Ben: I understand that Java primitive types do also have constructors. – BoltClock Oct 31 '17 at 01:34
Thanks. But why in https://stackoverflow.com/a/47024170 `new` can't apply to `int`. – Oct 31 '17 at 01:54
@Ben: Because Java doesn't allow it? – BoltClock Oct 31 '17 at 01:56
How can you show that `int` in Java has constructor? – Oct 31 '17 at 01:57

Soner Gönül · Answer 2 · 2017-10-30T06:12:55.677

new operator doesn't mean that it can be used only for reference types. It can be used with value types also.

From new Operator

Used to create objects and invoke constructors.

Since every value type implicitly has a public default constructor, all value types has default values. You can read Default Values Table.

For example;

int i = new int(); // i will be 0 for because its default values.

Default value for struct type;

The value produced by setting all value-type fields to their default values and all reference-type fields to null.

Also From MSDN:

When you create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the new operator. If you do not use new, the fields will remain unassigned and the object cannot be used until all of the fields are initialized.

+1 as fast, for the msdn link. Maybe remove the `(v=vs.71)` part? — Ken Kin, Mar 23 '13 at 17:59

score 4 · Answer 3 · answered Mar 23 '13 at 17:56

4

You can "new" an integer as well.
The difference is you CANT pass a reference class by value.

answered Mar 23 '13 at 17:56

Yochai Timmer

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score 3 · Answer 4 · answered Mar 23 '13 at 17:56

3

It says right here in the MSDN document, the new operator is used to invoke the default constructor of a value type.

answered Mar 23 '13 at 17:56

score 1 · Answer 5 · answered Mar 23 '13 at 17:56

1

You don't have to use the new operator to create a struct. If you do it will call its constructor, if you don't all field will remain unassigned.

answered Mar 23 '13 at 17:56

Daniel Wardin

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If a struct is a value type why can I new it?

5 Answers5