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On Friday, 7 May 2021 at 11:55:53 UTC, Andrei Alexandrescu wrote:
>On 5/7/21 2:03 AM, evilrat wrote:
>On Friday, 7 May 2021 at 03:48:47 UTC, Andrei Alexandrescu wrote:
>We should remove all that rot from phobos pronto.
Just a commoner here, can you explain for stupid what makes enum string a no go and why it should begone?
Heavy toll on the infra for a very niche use case with trivial workarounds on the user side.
To try to put some focus on the user perspective, here's a sample program:
import std.stdio;
import std.array;
import std.range;
void main()
{
writefln!"%d"(0);
immutable string f1 = "%d";
writefln!f1(1);
enum f2 = "%d";
writefln!f2(2);
enum string f3 = "%d";
writefln!f3(3);
enum { f4 = "%d" }
writefln!f4(4);
enum : string { f5 = "%d" }
writefln!f5(5);
enum X { f6 = "%d" }
writefln!(X.f6)(6); // Compilation error
enum Y : string { f7 = "%d" }
writefln!(Y.f7)(7); // Compilation error
}
All but the named enums (last two) are fine. These fail with similar compilation errors:
Error: template std.stdio.writefln cannot deduce function from argument types !("%d")(int), candidates are:
dmd-2.095.1/osx/bin/../../src/phobos/std/stdio.d(4258): writefln(alias fmt, A...)(A args)
with fmt = f6,
A = (int)
must satisfy the following constraint:
isSomeString!(typeof(fmt))
dmd-2.095.1/osx/bin/../../src/phobos/std/stdio.d(4269): writefln(Char, A...)(in Char[] fmt, A args
This is at least a potentially confusing situation for users. The error message indicates that f6 should be a "string" of some kind, and it looks like one. One needs to be very familiar with the details to understand why it does not satisfy isSomeString. Similarly with understanding why anonymous enums are fine but named enums are not.
The error message is also not particularly helpful in determining what the available workarounds are. They may be trivial once understood, but there's non-trivial learning to get there. Note that slicing ([]) and .representation() do not work for the template argument. Casting does. e.g. The following is fine:
writefln!(cast(string)X.f6)(6);
It can be argued that this case is rare enough in user code that the ROI from either making the case work or improving the compiler error message is too low to devote time to this now. But maybe there are other cheap options that could help users. A documentation note perhaps. A FAQ somewhere on the D site that would surface in searches.
