• ref2401 (10/10) Mar 13 2014 Hi.
• w0rp (7/17) Mar 13 2014 enum is a compile-time constant. 'static immutable' is an
• ref2401 (1/1) Mar 13 2014 thank you
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (16/26) Mar 13 2014 enum defines a manifest constant, meaning that it is just a value; there...

"ref2401" <refactor24 gmail.com> writes:

Hi.
I have this structure:

struct MyStruct {
	enum MyStruct VALUE = MyStruct(5f);

	static immutable MyStruct value = MyStruct(5f);


	float data;

	this(float v) { data = v; }
}

What's the difference between MyStruct.VALUE and MyStruct.value? 
How should I decide what to use?

"w0rp" <devw0rp gmail.com> writes:

On Thursday, 13 March 2014 at 14:38:27 UTC, ref2401 wrote:
 Hi.
 I have this structure:

 struct MyStruct {
 	enum MyStruct VALUE = MyStruct(5f);

 	static immutable MyStruct value = MyStruct(5f);


 	float data;

 	this(float v) { data = v; }
 }

 What's the difference between MyStruct.VALUE and 
 MyStruct.value? How should I decide what to use?

enum is a compile-time constant. 'static immutable' is an 
immutable (and therefore implicitly shared between threads...) 
runtime constant that isn't part of the struct itself. I'd stick 
with enum and switch to static when what you're writing becomes 
impossible to express at compile-time. A surprising number of 
things can actually be expressed at compile-time.

"ref2401" <refactor24 gmail.com> writes:

thank you

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 03/13/2014 07:38 AM, ref2401 wrote:

 Hi.
 I have this structure:

 struct MyStruct {
      enum MyStruct VALUE = MyStruct(5f);

      static immutable MyStruct value = MyStruct(5f);


      float data;

      this(float v) { data = v; }
 }

 What's the difference between MyStruct.VALUE and MyStruct.value? How
 should I decide what to use?

enum defines a manifest constant, meaning that it is just a value; there 
is not one but many MyStruct objects constructed every time VALUE is 
used in the code. The following run-time asserts prove that two 
instances have different data members:

     assert(&MyStruct.VALUE.data != &MyStruct.VALUE.data);

On the other hand, there is just one MyStruct.value object:

     assert(&MyStruct.value == &MyStruct.value);

In other words, MyStruct.VALUE is an rvalue but MyStruct.value is an 
lvalue; you cannot take the address of an rvalue. The following static 
asserts pass.

     static assert(!__traits(compiles, &MyStruct.VALUE));
     static assert( __traits(compiles, &MyStruct.value));

It shouldn't matter much for such a type but prefer a static immutable 
for expensive types like arrays.

Ali