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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
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
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
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
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
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