On 09/10/2012 01:20 AM, timotheecour wrote:
I'd like to achieve the following:
----
import std.stdio,std.range,std.algorithm,std.array;
void main(){
auto dg=a=>a*2;
auto a=iota(0,10);
writeln(a.map!dg.array);
}
----
but this doesn't compile:
Error: variable [...]dg type void is inferred from initializer delegate
(__T26 a)
{
return a * 2;
}
, and variables cannot be of type void
However this works:
writeln(a.map!(a=>a*2).array);
but I want to reuse dg in other expressions (and avoid repeating myself)
Also, I want to avoid using string litteral enum dg=`a*2` as in my case
dg is much more complicated and this is cleaner without a string IMHO.
My questions:
1) why can't the compiler infer the type int(int) for dg?
Because it can't. D unfortunately does not have powerful type inference.
2) how to convert a lambda a=>a*2 to a delegate or function?
Those need full type information. The lambda as shown is generic.
3) if 2 is not possible, how to achieve what I'm trying to do WITHOUT
having to make the type explicit as in "int delegate(int) dg=(int
a){return a*2;}"?
template ID(alias a){ alias a ID; }
void main(){
alias ID!(a=>a*2) dg;
auto a=iota(0,10);
writeln(a.map!dg.array);
}
4) is there a way to have template delegates, and what's the syntax in
this simple example?
Already shown.
