• Marcin Szymczak (37/37) Aug 11 2015 When programming i have encountered a simple ( i think ) problem,
• Adam D. Ruppe (4/10) Aug 11 2015 I don't think to! with the base given works on the chunked
• wobbles (21/24) Aug 12 2015 I think writing a simple function to parse a string into a Color

"Marcin Szymczak" <m_szymczak o2.pl> writes:

When programming i have encountered a simple ( i think ) problem, 
yet i can't get my head around it. I am trying to convert a 
string ( like "#FF00FF" for magenta ) into a color. I figured out 

"chunks" range convert each pair of 2 chars into a number and 
assign it to specific component. The snippet looks like this

	Color color;
	auto chunk = chunks( str[1..$], 2 );
	color.r = to!ubyte( chunk.front, 16 ); chunk.popFront;
	color.g = to!ubyte( chunk.front, 16 ); chunk.popFront;
	color.b = to!ubyte( chunk.front, 16 ); chunk.popFront;

But the compilation fails, stating

/usr/include/dlang/dmd/std/conv.d(295): Error: template 
std.conv.toImpl cannot deduce function from argument types 
!(ubyte)(Take!string, int), candidates are:
/usr/include/dlang/dmd/std/conv.d(361):        std.conv.toImpl(T, 
S)(S value) if (isImplicitlyConvertible!(S, T) && 
!isEnumStrToStr!(S, T) && !isNullToStr!(S, T))
/usr/include/dlang/dmd/std/conv.d(475):        std.conv.toImpl(T, 
S)(ref S s) if (isRawStaticArray!S)
/usr/include/dlang/dmd/std/conv.d(491):        std.conv.toImpl(T, 
S)(S value) if (!isImplicitlyConvertible!(S, T) && 
is(typeof(S.init.opCast!T()) : T) && !isExactSomeString!T && 
!is(typeof(T(value))))
/usr/include/dlang/dmd/std/conv.d(542):        std.conv.toImpl(T, 
S)(S value) if (!isImplicitlyConvertible!(S, T) && is(T == 
struct) && is(typeof(T(value))))
/usr/include/dlang/dmd/std/conv.d(591):        std.conv.toImpl(T, 
S)(S value) if (!isImplicitlyConvertible!(S, T) && is(T == class) 
&& is(typeof(new T(value))))
/usr/include/dlang/dmd/std/conv.d(295):        ... (9 more, -v to 
show) ...
source/engine/graphics/core.d(43): Error: template instance 
std.conv.to!ubyte.to!(Take!string, int) error instantiating

I would really love to solve this problem using ranges, because i 
am learning how to use them. Unfortunately even such a simple 
task seems so hard for me ;(

"Adam D. Ruppe" <destructionator gmail.com> writes:

On Tuesday, 11 August 2015 at 22:11:51 UTC, Marcin Szymczak wrote:
 /usr/include/dlang/dmd/std/conv.d(295): Error: template 
 std.conv.toImpl cannot deduce function from argument types 
 !(ubyte)(Take!string, int), candidates are:


I don't think to! with the base given works on the chunked 
ranges, it just works on regular strings.

 I would really love to solve this problem using ranges, because 
 i am learning how to use them. Unfortunately even such a simple 
 task seems so hard for me ;(

meh, I'd just slice the string.

"wobbles" <grogan.colin gmail.com> writes:

On Tuesday, 11 August 2015 at 22:11:51 UTC, Marcin Szymczak wrote:

 I would really love to solve this problem using ranges, because 
 i am learning how to use them. Unfortunately even such a simple 
 task seems so hard for me ;(

I think writing a simple function to parse a string into a Color 
would be best here.

Color parseRGBString(string theString){
         if(theString.length != 7)
                 throw new Exception("Error. Cannot parse to 
color: " ~ theString);
         return Color(
                 to!ubyte(theString[1..3], 16),
                 to!ubyte(theString[3..5], 16),
                 to!ubyte(theString[5..7], 16)
         );
}

I could probably do more to ensure that the string actually does 
represent a color (e.g. Check if no char is > F etc).

Also, using ranges isn't always required, theres no such thing as 
a "too simple" solution, as long as it works!

You can use this in a range then, e.g. say the user passes in 
lots of strings to your program, you can

listOfColors.map!(a => a.parseRGBString); // and now you have a 
lazily evaluated list of Color objects.