On Wednesday, 24 June 2015 at 08:18:52 UTC, Stefan wrote:
I tried to refactor some existing code to use more of the
functional patterns/style (map, filter, reduce, ..).
The task is to read in some sort of a simple property file and
present the result as an associative array.
My attempt is:
import std.stdio;
import std.algorithm.iteration : filter, map, reduce;
import std.algorithm.mutation : split;
import std.string : indexOf, strip;
import std.stdio : File, writeln;
import std.algorithm : startsWith;
string[string] add( ref string[string] result, in string line) {
int assignmentIndex = indexOf( line, "=" );
if ( assignmentIndex > 0 ) {
string key = line[ 0 .. assignmentIndex ];
string value = line[ assignmentIndex + 1 .. line.length
];
result[ key ] = value;
}
return result;
}
void main() {
auto input = File( "test.ini", "r" );
auto lines = input.byLine()
.filter!( line => !startsWith( line, "#" ) &&
!startsWith( line, "!") && line.length > 0 )
.map!( line => strip( line ) );
string[string] props;
auto result = reduce!(add)( props, lines );
}
result should now contain the associative array.
However, it fails with an error in the "reduce" line:
c:\develop\dmd2.067.1\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(2536):
Error: static assert "Incompatible function/seed/element:
prop.add/string[string]/char[]"
c:\develop\dmd2.067.1\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(2521):
instantiated from here: reduceImpl!(false, MapResult!(__lambda2,
FilterResult!(__lambda1, ByLine!(char, char))), string[string])
c:\develop\dmd2.067.1\windows\bin\..\..\src\phobos\std\algorithm\iteration.d(2505):
instantiated from here: reducePreImpl!(MapResult!(__lambda2,
FilterResult!(__lambda1, ByLine!(char, char))), string[string])
source\prop.d(30): instantiated from here:
reduce!(string[string], MapResult!(__lambda2,
FilterResult!(__lambda1, ByLine!(char, char))))
I have no idea how to resolve this.
input.byLine() yields char[]'s as range elements, while props is
(correctly) indexed by strings, i.e. immutable(char)[]. Use .idup
to create an immutable copy of the property name, e.g.:
auto lines = input.byLine()
.filter!( line => !startsWith( line, "#" ) && !startsWith(
line, "!") && line.length > 0 )
.map!( line => strip( line.idup ) );
