On Saturday, 30 September 2017 at 17:17:17 UTC, SrMordred wrote:
writeln( "a.b.c".splitter('.').dropBack(1) ); //compiles ok
writeln( "a.b.c".splitter(".").dropBack(1) );
//error:
Error: template std.range.dropBack cannot deduce function from
argument types !()(Result, int), candidates are:
(...)
Hm.. can someone explain whats going on?
It's easy to overlook, but documentation for splitter starts out:
Lazily splits a range using an element as a separator.
An element of a string is a char, not a string. It needs to be
read somewhat literally, but it is correct.
It's also part of template constraint, useful once you've become
accustomed to reading them:
auto splitter(alias pred = "a == b", Range, Separator)(Range
r, Separator s)
if (is(typeof(binaryFun!pred(r.front, s)) : bool) && ....
For "a.b.c"splitter(x), Range r is a string, r.front is a char.
The template can only be instantiated if the predicate function
is valid. The predicate function is "a == b". Since r.front is a
char, then s must be a type that can be compared with '=='. A
string and char cannot be compared with '==', which is why the a
valid template instantiation could not be found.
