Re: Why this template code does not compile?
On Wednesday, 13 March 2019 at 17:38:02 UTC, Victor Porton wrote:
Why this template code does not compile?
///
module runnable;
import std.meta;
import std.typecons;
template FieldInfo(argT, string argName) {
template FieldInfo(Nullable!argT argDefault =
Nullable!argT()) {
}
}
alias processFields(T, string name) =
AliasSeq!(FieldInfo!(T, name)());
The inner `FieldInfo` template isn't a function, but by adding a
second set of parentheses after `(T, name)`, you're attempting to
call it as one.
If you want to instantiate the inner template with its default
argument, you can use `std.meta.Instantiate`:
alias processFields(T, string name) =
AliasSeq!(Instantiate!(FieldInfo!(T, name)));
Why this template code does not compile?
Why this template code does not compile?
///
module runnable;
import std.meta;
import std.typecons;
template FieldInfo(argT, string argName) {
template FieldInfo(Nullable!argT argDefault =
Nullable!argT()) {
}
}
alias processFields(T, string name) =
AliasSeq!(FieldInfo!(T, name)());
void main(string[] args)
{
alias Fields = processFields!(int, "x");
}
///
/tmp/temp_7F58BE2F0150.d(12,34): Error: template
`runnable.FieldInfo!(int, "x").FieldInfo` cannot deduce function
from argument types `!()()`, candidates are:
/tmp/temp_7F58BE2F0150.d(7,5):`runnable.FieldInfo!(int,
"x").FieldInfo(Nullable!int argDefault = Nullable!argT())`
/tmp/temp_7F58BE2F0150.d(16,20): Error: template instance
`runnable.processFields!(int, "x")` error instantiating
LDC - the LLVM D compiler (1.11.0):
based on DMD v2.081.2 and LLVM 6.0.1
