On Wednesday, 28 May 2014 at 23:27:34 UTC, bearophile wrote:
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
IMHO something like this is better:
class MyException : Exception
{
private char[20] index_buff; // should be enough for
size_t.max
this(string msg, size_t index, string file = __FILE__, size_t
line = __LINE__, Throwable next = null)
{
super(msg, file, line, next);
// in-place conversion of size_t to char[]
}
void toString(void delegate(const(char)[]) sink) const
{
sink(msg);
sink(" (at index ");
sink(index_buff);
sink(")");
}
}
Benefits: no arbitrary message length limit, no string
construction unless toString is actually called.
