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digitalmars.D.learn - Alias on an array element

reply solidstate1991 <laszloszeremi outlook.com> writes:
I'm making a struct for easy color handling Here's a code sample:

ublic struct Color{
	union{
		uint raw;	///Raw representation in integer form, also forces 
the system to align in INT32.
		ubyte[4] colors;	///Normal representation, aliases are used for 
color naming.
		ubyte alpha, red, green, blue;
	}
	version(LittleEndian){
		alias alpha = colors[0];
		alias red = colors[1];
		alias green = colors[2];
		alias blue = colors[3];
	}else{
		alias alpha = colors[3];
		alias red = colors[2];
		alias green = colors[1];
		alias blue = colors[0];
	}
}

All the aliases are fail to compile, have not found anything 
about it in any of the documentations I checked.
Oct 12 2017
next sibling parent reply solidstate1991 <laszloszeremi outlook.com> writes:
On Friday, 13 October 2017 at 01:09:56 UTC, solidstate1991 wrote:

 I'm making a struct for easy color handling Here's a code 
 sample:

 ublic struct Color{
 	union{
 		uint raw;	///Raw representation in integer form, also forces 
 the system to align in INT32.
 		ubyte[4] colors;	///Normal representation, aliases are used 
 for color naming.
 		ubyte alpha, red, green, blue;
 	}
 	version(LittleEndian){
 		alias alpha = colors[0];
 		alias red = colors[1];
 		alias green = colors[2];
 		alias blue = colors[3];
 	}else{
 		alias alpha = colors[3];
 		alias red = colors[2];
 		alias green = colors[1];
 		alias blue = colors[0];
 	}
 }

 All the aliases are fail to compile, have not found anything 
 about it in any of the documentations I checked.


Edit: ubyte alpha, red, green, blue; was added so I can continue 
debugging after the refactoring until I find a solution.
Oct 12 2017
parent reply Meta <jared771 gmail.com> writes:
On Friday, 13 October 2017 at 01:12:38 UTC, solidstate1991 wrote:

 On Friday, 13 October 2017 at 01:09:56 UTC, solidstate1991 
 wrote:

 I'm making a struct for easy color handling Here's a code 
 sample:

 ublic struct Color{
 	union{
 		uint raw;	///Raw representation in integer form, also forces 
 the system to align in INT32.
 		ubyte[4] colors;	///Normal representation, aliases are used 
 for color naming.
 		ubyte alpha, red, green, blue;
 	}
 	version(LittleEndian){
 		alias alpha = colors[0];
 		alias red = colors[1];
 		alias green = colors[2];
 		alias blue = colors[3];
 	}else{
 		alias alpha = colors[3];
 		alias red = colors[2];
 		alias green = colors[1];
 		alias blue = colors[0];
 	}
 }

 All the aliases are fail to compile, have not found anything 
 about it in any of the documentations I checked.


 Edit: ubyte alpha, red, green, blue; was added so I can 
 continue debugging after the refactoring until I find a 
 solution.


You can only create aliases for symbols, not expressions. You 
could create accessor functions that return the appropriate 
indices.
Oct 12 2017
parent Igor <stojkovic.igor gmail.com> writes:
On Friday, 13 October 2017 at 02:04:03 UTC, Meta wrote:

 On Friday, 13 October 2017 at 01:12:38 UTC, solidstate1991 
 wrote:

 On Friday, 13 October 2017 at 01:09:56 UTC, solidstate1991 
 wrote:

 I'm making a struct for easy color handling Here's a code 
 sample:

 ublic struct Color{
 	union{
 		uint raw;	///Raw representation in integer form, also 
 forces the system to align in INT32.
 		ubyte[4] colors;	///Normal representation, aliases are used 
 for color naming.
 		ubyte alpha, red, green, blue;
 	}
 	version(LittleEndian){
 		alias alpha = colors[0];
 		alias red = colors[1];
 		alias green = colors[2];
 		alias blue = colors[3];
 	}else{
 		alias alpha = colors[3];
 		alias red = colors[2];
 		alias green = colors[1];
 		alias blue = colors[0];
 	}
 }

 All the aliases are fail to compile, have not found anything 
 about it in any of the documentations I checked.


 Edit: ubyte alpha, red, green, blue; was added so I can 
 continue debugging after the refactoring until I find a 
 solution.


 You can only create aliases for symbols, not expressions. You 
 could create accessor functions that return the appropriate 
 indices.


Why not just do this:

version(LittleEndian) {
     ubyte alpha, red, green, blue;
} else {
     ubyte blue, green, red, alpha;
}

BTW. What platforms do you have in mind when thinking about 
BigEndian? I am curious because I usually consider BigEndian dead 
for my purposes.
Oct 13 2017
prev sibling parent reply Adam D. Ruppe <destructionator gmail.com> writes:
On Friday, 13 October 2017 at 01:09:56 UTC, solidstate1991 wrote:

 All the aliases are fail to compile, have not found anything 
 about it in any of the documentations I checked.


Like the others said, alias just renames symbols, not 
expressions. Think of the generated code - if you are replacing a 
  name, alias will work, but if you actually need to paste in some 
code that gets generated for each object, it won't.

With the member variables or arrays, it changes a bit for each 
object.


Alternatives here include:

* just put the ubytes in your union. That's how I'd do it. (in 
fact, that is how I did it: 
https://github.com/adamdruppe/arsd/blob/master/color.d#L128 )

	union {
		ubyte[4] components; /// [r, g, b, a]

		/// Holder for rgba individual components.
		struct {
			ubyte r; /// red
			ubyte g; /// green
			ubyte b; /// blue
			ubyte a; /// alpha. 255 == opaque
		}

		uint asUint; /// The components as a single 32 bit value 
(beware of endian issues!)
}


The anonymous struct wrapper inside the union is allowed and 
groups the 4 of them together as a single element inside the 
union.


* Use a  property ref function to return the array element and 
trust the compiler to inline it.
Oct 13 2017
parent Meta <jared771 gmail.com> writes:
On Friday, 13 October 2017 at 13:22:42 UTC, Adam D. Ruppe wrote:

 * Use a  property ref function to return the array element and 
 trust the compiler to inline it.


You could also use pragma(inline, true).
Oct 13 2017