Allow implicit string literal -> const(wchar_t)[]

[thewilsonator]

for druntime#2349

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[thewilsonator]

cc @rainers is this going to do what I think it does?

[nordlow]

Tests?

[Geod24]

Could you provide some context ? I'm not sure I follow the reasoning.

[thewilsonator]

enum foo : wchar { whatever }

immutable(foo) [] a = "something"; // fails

enum __c_wchar_t : wchar;
immutable(__c_wchar_t)[] b = "something"; // fails but as __c_wchar_t is magic, it should pass

__c_wchar_t is rather a lot less useful without this.

Also where are implicit conversions tested in the test suite?

[jacob-carlborg]

• Needs to have tests
• Needs to have a changelog entry
• Needs to have a spec update

[thewilsonator]

Needs to have a changelog entry
Needs to have a spec update

dlang/druntime#2349 Hmm, actually might be better to have it in DMD and fold the changelog for #8342 into it.

[thewilsonator]

How is the implicit conversion from e.g. string to const(char)* for string literals done? I can't seem to see anything in mtype.d.

[Geod24]

It's not that simple. Check the following snippet:

import core.stdc.stdio;
import core.stdc.string;
import core.stdc.errno;

import std.conv;
import std.stdio;

extern(C) int wprintf(const __c_wchar_t* format, ...);

enum __c_wchar_t : dchar; // Use `wchar` if you are on Windows

static immutable string foo = "Hello World   !\n";

void main ()
{
    immutable(__c_wchar_t)[] str = foo;
    if (-1 == wprintf(str.ptr))
        writeln("Error: ", strerror(errno).to!string);
}

This prints `Error: Illegal byte sequence" on my machine (OSX).
It's because this implicit conv is just blindly doing an array cast in this case. Removing one of the character will yield an "array cast misalignment" assert error.

There is no implicit conversion between {w,d}string and string, it's just that "foo" is not typed as string (but ""c is).

Side note: testing with literals is never enough.

[thewilsonator]

Ahh, right. Where is the string literal specific stuff handled? Not mtype.d apparently.

Added tests for non-literal conversion failure

[ibuclaw]

I see no one approving this, why was it merged?

[ibuclaw]

Indentation here looks off. I can't tell whether the early return here should be part of the first or second condition.

[ghost]

Change brought by #9460 would break the test added in the PR. Have a look if you have some time to @thewilsonator .