Some @nogc text conversion in Phobos?

[bearophile via Digitalmars-d]

This is currently accepted code:

void main() {
    import std.array: appender;
    import std.format: formattedWrite;

    auto writer = appender!string;
    formattedWrite(writer, "%s is the ultimate %s.", 42, 
"answer");
    assert(writer.data == "42 is the ultimate answer.");
}



But there are problems caused by formatting for exception error 
messages:
https://d.puremagic.com/issues/show_bug.cgi?id=12768


An example of the problem:

class UTFException : Exception
{
...
    pure @safe
    this(string msg, size_t index, string file = __FILE__, size_t 
line = __LINE__, Throwable next = null) {
        import std.string;
        super(msg ~ format(" (at index %s)", index), file, line, 
next);
    }


Because of that several Phobos functions can't be @nogc.

So is it a good idea to add to Phobos a function similar to this?


void main() pure nothrow @safe @nogc {
    import std.format: bufferText;

    immutable n = 42;
    immutable s = "answer";
    char[100] buf;
    const Nullable!(char[]) result =
        buf.bufferText(n, " is the ultimate ", s);
    assert(result.get == "42 is the ultimate answer.");
}



That should allow (in theory) code like:

class UTFException : Exception
{
...
    pure @safe @nogc
    this(in char[] msg, string file = __FILE__, size_t line = 
__LINE__, Throwable next = null) {
        super(msg, file, line, next);
    }

...

char[100] buf;
const msg = buf.bufferText("Invalid UTF-8 sequence (at index ", 
i, ')');
if (mgs.isNull)
    new UTFException("Invalid UTF-8 sequence")...
else
    new UTFException(msg.get)...



A problem left is that the ctor of Exception is not yet @pure 
@nothrow @safe @nogc.

Bye,
bearophile