You should open an issue on https://issues.dlang.org/

until it is fixed you can use lazy variation byChar, byWchar or byUTF:

void main()
{

import std.utf : byWchar;

import std.array : array;

wstring s = byWchar("abc").array;
}

On Wed, Aug 16, 2017 at 7:09 AM, apz28 via Digitalmars-d-learn <digitalmars-d-learn@puremagic.com> wrote:

void main()
{
import std.utf : toUTF16; // Same problem with toUTF8

wstring s = toUTF16!string("abc");
}

Compilation output:
/d500/f513.d(3): Deprecation: function std.utf.toUTF16 is deprecated - To be removed November 2017. Please use std.utf.encode instead.
/d500/f513.d(3): Deprecation: function std.utf.toUTF16 is deprecated - To be removed November 2017. Please use std.utf.encode instead.